vue/dist/vue.esm.browser.js

Reactive, component-oriented view layer for modern web interfaces.

/*!
 * Vue.js v2.6.14
 * (c) 2014-2021 Evan You
 * Released under the MIT License.
 */
/*  */

const emptyObject = Object.freeze({});

// These helpers produce better VM code in JS engines due to their
// explicitness and function inlining.
function isUndef (v) {
  return v === undefined || v === null
}

function isDef (v) {
  return v !== undefined && v !== null
}

function isTrue (v) {
  return v === true
}

function isFalse (v) {
  return v === false
}

/**
 * Check if value is primitive.
 */
function isPrimitive (value) {
  return (
    typeof value === 'string' ||
    typeof value === 'number' ||
    // $flow-disable-line
    typeof value === 'symbol' ||
    typeof value === 'boolean'
  )
}

/**
 * Quick object check - this is primarily used to tell
 * Objects from primitive values when we know the value
 * is a JSON-compliant type.
 */
function isObject (obj) {
  return obj !== null && typeof obj === 'object'
}

/**
 * Get the raw type string of a value, e.g., [object Object].
 */
const _toString = Object.prototype.toString;

function toRawType (value) {
  return _toString.call(value).slice(8, -1)
}

/**
 * Strict object type check. Only returns true
 * for plain JavaScript objects.
 */
function isPlainObject (obj) {
  return _toString.call(obj) === '[object Object]'
}

function isRegExp (v) {
  return _toString.call(v) === '[object RegExp]'
}

/**
 * Check if val is a valid array index.
 */
function isValidArrayIndex (val) {
  const n = parseFloat(String(val));
  return n >= 0 && Math.floor(n) === n && isFinite(val)
}

function isPromise (val) {
  return (
    isDef(val) &&
    typeof val.then === 'function' &&
    typeof val.catch === 'function'
  )
}

/**
 * Convert a value to a string that is actually rendered.
 */
function toString (val) {
  return val == null
    ? ''
    : Array.isArray(val) || (isPlainObject(val) && val.toString === _toString)
      ? JSON.stringify(val, null, 2)
      : String(val)
}

/**
 * Convert an input value to a number for persistence.
 * If the conversion fails, return original string.
 */
function toNumber (val) {
  const n = parseFloat(val);
  return isNaN(n) ? val : n
}

/**
 * Make a map and return a function for checking if a key
 * is in that map.
 */
function makeMap (
  str,
  expectsLowerCase
) {
  const map = Object.create(null);
  const list = str.split(',');
  for (let i = 0; i < list.length; i++) {
    map[list[i]] = true;
  }
  return expectsLowerCase
    ? val => map[val.toLowerCase()]
    : val => map[val]
}

/**
 * Check if a tag is a built-in tag.
 */
const isBuiltInTag = makeMap('slot,component', true);

/**
 * Check if an attribute is a reserved attribute.
 */
const isReservedAttribute = makeMap('key,ref,slot,slot-scope,is');

/**
 * Remove an item from an array.
 */
function remove (arr, item) {
  if (arr.length) {
    const index = arr.indexOf(item);
    if (index > -1) {
      return arr.splice(index, 1)
    }
  }
}

/**
 * Check whether an object has the property.
 */
const hasOwnProperty = Object.prototype.hasOwnProperty;
function hasOwn (obj, key) {
  return hasOwnProperty.call(obj, key)
}

/**
 * Create a cached version of a pure function.
 */
function cached (fn) {
  const cache = Object.create(null);
  return (function cachedFn (str) {
    const hit = cache[str];
    return hit || (cache[str] = fn(str))
  })
}

/**
 * Camelize a hyphen-delimited string.
 */
const camelizeRE = /-(\w)/g;
const camelize = cached((str) => {
  return str.replace(camelizeRE, (_, c) => c ? c.toUpperCase() : '')
});

/**
 * Capitalize a string.
 */
const capitalize = cached((str) => {
  return str.charAt(0).toUpperCase() + str.slice(1)
});

/**
 * Hyphenate a camelCase string.
 */
const hyphenateRE = /\B([A-Z])/g;
const hyphenate = cached((str) => {
  return str.replace(hyphenateRE, '-$1').toLowerCase()
});

/**
 * Simple bind polyfill for environments that do not support it,
 * e.g., PhantomJS 1.x. Technically, we don't need this anymore
 * since native bind is now performant enough in most browsers.
 * But removing it would mean breaking code that was able to run in
 * PhantomJS 1.x, so this must be kept for backward compatibility.
 */

/* istanbul ignore next */
function polyfillBind (fn, ctx) {
  function boundFn (a) {
    const l = arguments.length;
    return l
      ? l > 1
        ? fn.apply(ctx, arguments)
        : fn.call(ctx, a)
      : fn.call(ctx)
  }

  boundFn._length = fn.length;
  return boundFn
}

function nativeBind (fn, ctx) {
  return fn.bind(ctx)
}

const bind = Function.prototype.bind
  ? nativeBind
  : polyfillBind;

/**
 * Convert an Array-like object to a real Array.
 */
function toArray (list, start) {
  start = start || 0;
  let i = list.length - start;
  const ret = new Array(i);
  while (i--) {
    ret[i] = list[i + start];
  }
  return ret
}

/**
 * Mix properties into target object.
 */
function extend (to, _from) {
  for (const key in _from) {
    to[key] = _from[key];
  }
  return to
}

/**
 * Merge an Array of Objects into a single Object.
 */
function toObject (arr) {
  const res = {};
  for (let i = 0; i < arr.length; i++) {
    if (arr[i]) {
      extend(res, arr[i]);
    }
  }
  return res
}

/* eslint-disable no-unused-vars */

/**
 * Perform no operation.
 * Stubbing args to make Flow happy without leaving useless transpiled code
 * with ...rest (https://flow.org/blog/2017/05/07/Strict-Function-Call-Arity/).
 */
function noop (a, b, c) {}

/**
 * Always return false.
 */
const no = (a, b, c) => false;

/* eslint-enable no-unused-vars */

/**
 * Return the same value.
 */
const identity = (_) => _;

/**
 * Generate a string containing static keys from compiler modules.
 */
function genStaticKeys (modules) {
  return modules.reduce((keys, m) => {
    return keys.concat(m.staticKeys || [])
  }, []).join(',')
}

/**
 * Check if two values are loosely equal - that is,
 * if they are plain objects, do they have the same shape?
 */
function looseEqual (a, b) {
  if (a === b) return true
  const isObjectA = isObject(a);
  const isObjectB = isObject(b);
  if (isObjectA && isObjectB) {
    try {
      const isArrayA = Array.isArray(a);
      const isArrayB = Array.isArray(b);
      if (isArrayA && isArrayB) {
        return a.length === b.length && a.every((e, i) => {
          return looseEqual(e, b[i])
        })
      } else if (a instanceof Date && b instanceof Date) {
        return a.getTime() === b.getTime()
      } else if (!isArrayA && !isArrayB) {
        const keysA = Object.keys(a);
        const keysB = Object.keys(b);
        return keysA.length === keysB.length && keysA.every(key => {
          return looseEqual(a[key], b[key])
        })
      } else {
        /* istanbul ignore next */
        return false
      }
    } catch (e) {
      /* istanbul ignore next */
      return false
    }
  } else if (!isObjectA && !isObjectB) {
    return String(a) === String(b)
  } else {
    return false
  }
}

/**
 * Return the first index at which a loosely equal value can be
 * found in the array (if value is a plain object, the array must
 * contain an object of the same shape), or -1 if it is not present.
 */
function looseIndexOf (arr, val) {
  for (let i = 0; i < arr.length; i++) {
    if (looseEqual(arr[i], val)) return i
  }
  return -1
}

/**
 * Ensure a function is called only once.
 */
function once (fn) {
  let called = false;
  return function () {
    if (!called) {
      called = true;
      fn.apply(this, arguments);
    }
  }
}

const SSR_ATTR = 'data-server-rendered';

const ASSET_TYPES = [
  'component',
  'directive',
  'filter'
];

const LIFECYCLE_HOOKS = [
  'beforeCreate',
  'created',
  'beforeMount',
  'mounted',
  'beforeUpdate',
  'updated',
  'beforeDestroy',
  'destroyed',
  'activated',
  'deactivated',
  'errorCaptured',
  'serverPrefetch'
];

/*  */



var config = ({
  /**
   * Option merge strategies (used in core/util/options)
   */
  // $flow-disable-line
  optionMergeStrategies: Object.create(null),

  /**
   * Whether to suppress warnings.
   */
  silent: false,

  /**
   * Show production mode tip message on boot?
   */
  productionTip: "development" !== 'production',

  /**
   * Whether to enable devtools
   */
  devtools: "development" !== 'production',

  /**
   * Whether to record perf
   */
  performance: false,

  /**
   * Error handler for watcher errors
   */
  errorHandler: null,

  /**
   * Warn handler for watcher warns
   */
  warnHandler: null,

  /**
   * Ignore certain custom elements
   */
  ignoredElements: [],

  /**
   * Custom user key aliases for v-on
   */
  // $flow-disable-line
  keyCodes: Object.create(null),

  /**
   * Check if a tag is reserved so that it cannot be registered as a
   * component. This is platform-dependent and may be overwritten.
   */
  isReservedTag: no,

  /**
   * Check if an attribute is reserved so that it cannot be used as a component
   * prop. This is platform-dependent and may be overwritten.
   */
  isReservedAttr: no,

  /**
   * Check if a tag is an unknown element.
   * Platform-dependent.
   */
  isUnknownElement: no,

  /**
   * Get the namespace of an element
   */
  getTagNamespace: noop,

  /**
   * Parse the real tag name for the specific platform.
   */
  parsePlatformTagName: identity,

  /**
   * Check if an attribute must be bound using property, e.g. value
   * Platform-dependent.
   */
  mustUseProp: no,

  /**
   * Perform updates asynchronously. Intended to be used by Vue Test Utils
   * This will significantly reduce performance if set to false.
   */
  async: true,

  /**
   * Exposed for legacy reasons
   */
  _lifecycleHooks: LIFECYCLE_HOOKS
});

/*  */

/**
 * unicode letters used for parsing html tags, component names and property paths.
 * using https://www.w3.org/TR/html53/semantics-scripting.html#potentialcustomelementname
 * skipping \u10000-\uEFFFF due to it freezing up PhantomJS
 */
const unicodeRegExp = /a-zA-Z\u00B7\u00C0-\u00D6\u00D8-\u00F6\u00F8-\u037D\u037F-\u1FFF\u200C-\u200D\u203F-\u2040\u2070-\u218F\u2C00-\u2FEF\u3001-\uD7FF\uF900-\uFDCF\uFDF0-\uFFFD/;

/**
 * Check if a string starts with $ or _
 */
function isReserved (str) {
  const c = (str + '').charCodeAt(0);
  return c === 0x24 || c === 0x5F
}

/**
 * Define a property.
 */
function def (obj, key, val, enumerable) {
  Object.defineProperty(obj, key, {
    value: val,
    enumerable: !!enumerable,
    writable: true,
    configurable: true
  });
}

/**
 * Parse simple path.
 */
const bailRE = new RegExp(`[^${unicodeRegExp.source}.$_\\d]`);
function parsePath (path) {
  if (bailRE.test(path)) {
    return
  }
  const segments = path.split('.');
  return function (obj) {
    for (let i = 0; i < segments.length; i++) {
      if (!obj) return
      obj = obj[segments[i]];
    }
    return obj
  }
}

/*  */

// can we use __proto__?
const hasProto = '__proto__' in {};

// Browser environment sniffing
const inBrowser = typeof window !== 'undefined';
const inWeex = typeof WXEnvironment !== 'undefined' && !!WXEnvironment.platform;
const weexPlatform = inWeex && WXEnvironment.platform.toLowerCase();
const UA = inBrowser && window.navigator.userAgent.toLowerCase();
const isIE = UA && /msie|trident/.test(UA);
const isIE9 = UA && UA.indexOf('msie 9.0') > 0;
const isEdge = UA && UA.indexOf('edge/') > 0;
const isAndroid = (UA && UA.indexOf('android') > 0) || (weexPlatform === 'android');
const isIOS = (UA && /iphone|ipad|ipod|ios/.test(UA)) || (weexPlatform === 'ios');
const isChrome = UA && /chrome\/\d+/.test(UA) && !isEdge;
const isPhantomJS = UA && /phantomjs/.test(UA);
const isFF = UA && UA.match(/firefox\/(\d+)/);

// Firefox has a "watch" function on Object.prototype...
const nativeWatch = ({}).watch;

let supportsPassive = false;
if (inBrowser) {
  try {
    const opts = {};
    Object.defineProperty(opts, 'passive', ({
      get () {
        /* istanbul ignore next */
        supportsPassive = true;
      }
    })); // https://github.com/facebook/flow/issues/285
    window.addEventListener('test-passive', null, opts);
  } catch (e) {}
}

// this needs to be lazy-evaled because vue may be required before
// vue-server-renderer can set VUE_ENV
let _isServer;
const isServerRendering = () => {
  if (_isServer === undefined) {
    /* istanbul ignore if */
    if (!inBrowser && !inWeex && typeof global !== 'undefined') {
      // detect presence of vue-server-renderer and avoid
      // Webpack shimming the process
      _isServer = global['process'] && global['process'].env.VUE_ENV === 'server';
    } else {
      _isServer = false;
    }
  }
  return _isServer
};

// detect devtools
const devtools = inBrowser && window.__VUE_DEVTOOLS_GLOBAL_HOOK__;

/* istanbul ignore next */
function isNative (Ctor) {
  return typeof Ctor === 'function' && /native code/.test(Ctor.toString())
}

const hasSymbol =
  typeof Symbol !== 'undefined' && isNative(Symbol) &&
  typeof Reflect !== 'undefined' && isNative(Reflect.ownKeys);

let _Set;
/* istanbul ignore if */ // $flow-disable-line
if (typeof Set !== 'undefined' && isNative(Set)) {
  // use native Set when available.
  _Set = Set;
} else {
  // a non-standard Set polyfill that only works with primitive keys.
  _Set = class Set   {
    
    constructor () {
      this.set = Object.create(null);
    }
    has (key) {
      return this.set[key] === true
    }
    add (key) {
      this.set[key] = true;
    }
    clear () {
      this.set = Object.create(null);
    }
  };
}

/*  */

let warn = noop;
let tip = noop;
let generateComponentTrace = (noop); // work around flow check
let formatComponentName = (noop);

{
  const hasConsole = typeof console !== 'undefined';
  const classifyRE = /(?:^|[-_])(\w)/g;
  const classify = str => str
    .replace(classifyRE, c => c.toUpperCase())
    .replace(/[-_]/g, '');

  warn = (msg, vm) => {
    const trace = vm ? generateComponentTrace(vm) : '';

    if (config.warnHandler) {
      config.warnHandler.call(null, msg, vm, trace);
    } else if (hasConsole && (!config.silent)) {
      console.error(`[Vue warn]: ${msg}${trace}`);
    }
  };

  tip = (msg, vm) => {
    if (hasConsole && (!config.silent)) {
      console.warn(`[Vue tip]: ${msg}` + (
        vm ? generateComponentTrace(vm) : ''
      ));
    }
  };

  formatComponentName = (vm, includeFile) => {
    if (vm.$root === vm) {
      return '<Root>'
    }
    const options = typeof vm === 'function' && vm.cid != null
      ? vm.options
      : vm._isVue
        ? vm.$options || vm.constructor.options
        : vm;
    let name = options.name || options._componentTag;
    const file = options.__file;
    if (!name && file) {
      const match = file.match(/([^/\\]+)\.vue$/);
      name = match && match[1];
    }

    return (
      (name ? `<${classify(name)}>` : `<Anonymous>`) +
      (file && includeFile !== false ? ` at ${file}` : '')
    )
  };

  const repeat = (str, n) => {
    let res = '';
    while (n) {
      if (n % 2 === 1) res += str;
      if (n > 1) str += str;
      n >>= 1;
    }
    return res
  };

  generateComponentTrace = vm => {
    if (vm._isVue && vm.$parent) {
      const tree = [];
      let currentRecursiveSequence = 0;
      while (vm) {
        if (tree.length > 0) {
          const last = tree[tree.length - 1];
          if (last.constructor === vm.constructor) {
            currentRecursiveSequence++;
            vm = vm.$parent;
            continue
          } else if (currentRecursiveSequence > 0) {
            tree[tree.length - 1] = [last, currentRecursiveSequence];
            currentRecursiveSequence = 0;
          }
        }
        tree.push(vm);
        vm = vm.$parent;
      }
      return '\n\nfound in\n\n' + tree
        .map((vm, i) => `${
          i === 0 ? '---> ' : repeat(' ', 5 + i * 2)
        }${
          Array.isArray(vm)
            ? `${formatComponentName(vm[0])}... (${vm[1]} recursive calls)`
            : formatComponentName(vm)
        }`)
        .join('\n')
    } else {
      return `\n\n(found in ${formatComponentName(vm)})`
    }
  };
}

/*  */

let uid = 0;

/**
 * A dep is an observable that can have multiple
 * directives subscribing to it.
 */
class Dep {
  
  
  

  constructor () {
    this.id = uid++;
    this.subs = [];
  }

  addSub (sub) {
    this.subs.push(sub);
  }

  removeSub (sub) {
    remove(this.subs, sub);
  }

  depend () {
    if (Dep.target) {
      Dep.target.addDep(this);
    }
  }

  notify () {
    // stabilize the subscriber list first
    const subs = this.subs.slice();
    if (!config.async) {
      // subs aren't sorted in scheduler if not running async
      // we need to sort them now to make sure they fire in correct
      // order
      subs.sort((a, b) => a.id - b.id);
    }
    for (let i = 0, l = subs.length; i < l; i++) {
      subs[i].update();
    }
  }
}

// The current target watcher being evaluated.
// This is globally unique because only one watcher
// can be evaluated at a time.
Dep.target = null;
const targetStack = [];

function pushTarget (target) {
  targetStack.push(target);
  Dep.target = target;
}

function popTarget () {
  targetStack.pop();
  Dep.target = targetStack[targetStack.length - 1];
}

/*  */

class VNode {
  
  
  
  
  
  
   // rendered in this component's scope
  
  
   // component instance
   // component placeholder node

  // strictly internal
   // contains raw HTML? (server only)
   // hoisted static node
   // necessary for enter transition check
   // empty comment placeholder?
   // is a cloned node?
   // is a v-once node?
   // async component factory function
  
  
  
   // real context vm for functional nodes
   // for SSR caching
   // used to store functional render context for devtools
   // functional scope id support

  constructor (
    tag,
    data,
    children,
    text,
    elm,
    context,
    componentOptions,
    asyncFactory
  ) {
    this.tag = tag;
    this.data = data;
    this.children = children;
    this.text = text;
    this.elm = elm;
    this.ns = undefined;
    this.context = context;
    this.fnContext = undefined;
    this.fnOptions = undefined;
    this.fnScopeId = undefined;
    this.key = data && data.key;
    this.componentOptions = componentOptions;
    this.componentInstance = undefined;
    this.parent = undefined;
    this.raw = false;
    this.isStatic = false;
    this.isRootInsert = true;
    this.isComment = false;
    this.isCloned = false;
    this.isOnce = false;
    this.asyncFactory = asyncFactory;
    this.asyncMeta = undefined;
    this.isAsyncPlaceholder = false;
  }

  // DEPRECATED: alias for componentInstance for backwards compat.
  /* istanbul ignore next */
  get child () {
    return this.componentInstance
  }
}

const createEmptyVNode = (text = '') => {
  const node = new VNode();
  node.text = text;
  node.isComment = true;
  return node
};

function createTextVNode (val) {
  return new VNode(undefined, undefined, undefined, String(val))
}

// optimized shallow clone
// used for static nodes and slot nodes because they may be reused across
// multiple renders, cloning them avoids errors when DOM manipulations rely
// on their elm reference.
function cloneVNode (vnode) {
  const cloned = new VNode(
    vnode.tag,
    vnode.data,
    // #7975
    // clone children array to avoid mutating original in case of cloning
    // a child.
    vnode.children && vnode.children.slice(),
    vnode.text,
    vnode.elm,
    vnode.context,
    vnode.componentOptions,
    vnode.asyncFactory
  );
  cloned.ns = vnode.ns;
  cloned.isStatic = vnode.isStatic;
  cloned.key = vnode.key;
  cloned.isComment = vnode.isComment;
  cloned.fnContext = vnode.fnContext;
  cloned.fnOptions = vnode.fnOptions;
  cloned.fnScopeId = vnode.fnScopeId;
  cloned.asyncMeta = vnode.asyncMeta;
  cloned.isCloned = true;
  return cloned
}

/*
 * not type checking this file because flow doesn't play well with
 * dynamically accessing methods on Array prototype
 */

const arrayProto = Array.prototype;
const arrayMethods = Object.create(arrayProto);

const methodsToPatch = [
  'push',
  'pop',
  'shift',
  'unshift',
  'splice',
  'sort',
  'reverse'
];

/**
 * Intercept mutating methods and emit events
 */
methodsToPatch.forEach(function (method) {
  // cache original method
  const original = arrayProto[method];
  def(arrayMethods, method, function mutator (...args) {
    const result = original.apply(this, args);
    const ob = this.__ob__;
    let inserted;
    switch (method) {
      case 'push':
      case 'unshift':
        inserted = args;
        break
      case 'splice':
        inserted = args.slice(2);
        break
    }
    if (inserted) ob.observeArray(inserted);
    // notify change
    ob.dep.notify();
    return result
  });
});

/*  */

const arrayKeys = Object.getOwnPropertyNames(arrayMethods);

/**
 * In some cases we may want to disable observation inside a component's
 * update computation.
 */
let shouldObserve = true;

function toggleObserving (value) {
  shouldObserve = value;
}

/**
 * Observer class that is attached to each observed
 * object. Once attached, the observer converts the target
 * object's property keys into getter/setters that
 * collect dependencies and dispatch updates.
 */
class Observer {
  
  
   // number of vms that have this object as root $data

  constructor (value) {
    this.value = value;
    this.dep = new Dep();
    this.vmCount = 0;
    def(value, '__ob__', this);
    if (Array.isArray(value)) {
      if (hasProto) {
        protoAugment(value, arrayMethods);
      } else {
        copyAugment(value, arrayMethods, arrayKeys);
      }
      this.observeArray(value);
    } else {
      this.walk(value);
    }
  }

  /**
   * Walk through all properties and convert them into
   * getter/setters. This method should only be called when
   * value type is Object.
   */
  walk (obj) {
    const keys = Object.keys(obj);
    for (let i = 0; i < keys.length; i++) {
      defineReactive$$1(obj, keys[i]);
    }
  }

  /**
   * Observe a list of Array items.
   */
  observeArray (items) {
    for (let i = 0, l = items.length; i < l; i++) {
      observe(items[i]);
    }
  }
}

// helpers

/**
 * Augment a target Object or Array by intercepting
 * the prototype chain using __proto__
 */
function protoAugment (target, src) {
  /* eslint-disable no-proto */
  target.__proto__ = src;
  /* eslint-enable no-proto */
}

/**
 * Augment a target Object or Array by defining
 * hidden properties.
 */
/* istanbul ignore next */
function copyAugment (target, src, keys) {
  for (let i = 0, l = keys.length; i < l; i++) {
    const key = keys[i];
    def(target, key, src[key]);
  }
}

/**
 * Attempt to create an observer instance for a value,
 * returns the new observer if successfully observed,
 * or the existing observer if the value already has one.
 */
function observe (value, asRootData) {
  if (!isObject(value) || value instanceof VNode) {
    return
  }
  let ob;
  if (hasOwn(value, '__ob__') && value.__ob__ instanceof Observer) {
    ob = value.__ob__;
  } else if (
    shouldObserve &&
    !isServerRendering() &&
    (Array.isArray(value) || isPlainObject(value)) &&
    Object.isExtensible(value) &&
    !value._isVue
  ) {
    ob = new Observer(value);
  }
  if (asRootData && ob) {
    ob.vmCount++;
  }
  return ob
}

/**
 * Define a reactive property on an Object.
 */
function defineReactive$$1 (
  obj,
  key,
  val,
  customSetter,
  shallow
) {
  const dep = new Dep();

  const property = Object.getOwnPropertyDescriptor(obj, key);
  if (property && property.configurable === false) {
    return
  }

  // cater for pre-defined getter/setters
  const getter = property && property.get;
  const setter = property && property.set;
  if ((!getter || setter) && arguments.length === 2) {
    val = obj[key];
  }

  let childOb = !shallow && observe(val);
  Object.defineProperty(obj, key, {
    enumerable: true,
    configurable: true,
    get: function reactiveGetter () {
      const value = getter ? getter.call(obj) : val;
      if (Dep.target) {
        dep.depend();
        if (childOb) {
          childOb.dep.depend();
          if (Array.isArray(value)) {
            dependArray(value);
          }
        }
      }
      return value
    },
    set: function reactiveSetter (newVal) {
      const value = getter ? getter.call(obj) : val;
      /* eslint-disable no-self-compare */
      if (newVal === value || (newVal !== newVal && value !== value)) {
        return
      }
      /* eslint-enable no-self-compare */
      if (customSetter) {
        customSetter();
      }
      // #7981: for accessor properties without setter
      if (getter && !setter) return
      if (setter) {
        setter.call(obj, newVal);
      } else {
        val = newVal;
      }
      childOb = !shallow && observe(newVal);
      dep.notify();
    }
  });
}

/**
 * Set a property on an object. Adds the new property and
 * triggers change notification if the property doesn't
 * already exist.
 */
function set (target, key, val) {
  if (isUndef(target) || isPrimitive(target)
  ) {
    warn(`Cannot set reactive property on undefined, null, or primitive value: ${(target)}`);
  }
  if (Array.isArray(target) && isValidArrayIndex(key)) {
    target.length = Math.max(target.length, key);
    target.splice(key, 1, val);
    return val
  }
  if (key in target && !(key in Object.prototype)) {
    target[key] = val;
    return val
  }
  const ob = (target).__ob__;
  if (target._isVue || (ob && ob.vmCount)) {
    warn(
      'Avoid adding reactive properties to a Vue instance or its root $data ' +
      'at runtime - declare it upfront in the data option.'
    );
    return val
  }
  if (!ob) {
    target[key] = val;
    return val
  }
  defineReactive$$1(ob.value, key, val);
  ob.dep.notify();
  return val
}

/**
 * Delete a property and trigger change if necessary.
 */
function del (target, key) {
  if (isUndef(target) || isPrimitive(target)
  ) {
    warn(`Cannot delete reactive property on undefined, null, or primitive value: ${(target)}`);
  }
  if (Array.isArray(target) && isValidArrayIndex(key)) {
    target.splice(key, 1);
    return
  }
  const ob = (target).__ob__;
  if (target._isVue || (ob && ob.vmCount)) {
    warn(
      'Avoid deleting properties on a Vue instance or its root $data ' +
      '- just set it to null.'
    );
    return
  }
  if (!hasOwn(target, key)) {
    return
  }
  delete target[key];
  if (!ob) {
    return
  }
  ob.dep.notify();
}

/**
 * Collect dependencies on array elements when the array is touched, since
 * we cannot intercept array element access like property getters.
 */
function dependArray (value) {
  for (let e, i = 0, l = value.length; i < l; i++) {
    e = value[i];
    e && e.__ob__ && e.__ob__.dep.depend();
    if (Array.isArray(e)) {
      dependArray(e);
    }
  }
}

/*  */

/**
 * Option overwriting strategies are functions that handle
 * how to merge a parent option value and a child option
 * value into the final value.
 */
const strats = config.optionMergeStrategies;

/**
 * Options with restrictions
 */
{
  strats.el = strats.propsData = function (parent, child, vm, key) {
    if (!vm) {
      warn(
        `option "${key}" can only be used during instance ` +
        'creation with the `new` keyword.'
      );
    }
    return defaultStrat(parent, child)
  };
}

/**
 * Helper that recursively merges two data objects together.
 */
function mergeData (to, from) {
  if (!from) return to
  let key, toVal, fromVal;

  const keys = hasSymbol
    ? Reflect.ownKeys(from)
    : Object.keys(from);

  for (let i = 0; i < keys.length; i++) {
    key = keys[i];
    // in case the object is already observed...
    if (key === '__ob__') continue
    toVal = to[key];
    fromVal = from[key];
    if (!hasOwn(to, key)) {
      set(to, key, fromVal);
    } else if (
      toVal !== fromVal &&
      isPlainObject(toVal) &&
      isPlainObject(fromVal)
    ) {
      mergeData(toVal, fromVal);
    }
  }
  return to
}

/**
 * Data
 */
function mergeDataOrFn (
  parentVal,
  childVal,
  vm
) {
  if (!vm) {
    // in a Vue.extend merge, both should be functions
    if (!childVal) {
      return parentVal
    }
    if (!parentVal) {
      return childVal
    }
    // when parentVal & childVal are both present,
    // we need to return a function that returns the
    // merged result of both functions... no need to
    // check if parentVal is a function here because
    // it has to be a function to pass previous merges.
    return function mergedDataFn () {
      return mergeData(
        typeof childVal === 'function' ? childVal.call(this, this) : childVal,
        typeof parentVal === 'function' ? parentVal.call(this, this) : parentVal
      )
    }
  } else {
    return function mergedInstanceDataFn () {
      // instance merge
      const instanceData = typeof childVal === 'function'
        ? childVal.call(vm, vm)
        : childVal;
      const defaultData = typeof parentVal === 'function'
        ? parentVal.call(vm, vm)
        : parentVal;
      if (instanceData) {
        return mergeData(instanceData, defaultData)
      } else {
        return defaultData
      }
    }
  }
}

strats.data = function (
  parentVal,
  childVal,
  vm
) {
  if (!vm) {
    if (childVal && typeof childVal !== 'function') {
      warn(
        'The "data" option should be a function ' +
        'that returns a per-instance value in component ' +
        'definitions.',
        vm
      );

      return parentVal
    }
    return mergeDataOrFn(parentVal, childVal)
  }

  return mergeDataOrFn(parentVal, childVal, vm)
};

/**
 * Hooks and props are merged as arrays.
 */
function mergeHook (
  parentVal,
  childVal
) {
  const res = childVal
    ? parentVal
      ? parentVal.concat(childVal)
      : Array.isArray(childVal)
        ? childVal
        : [childVal]
    : parentVal;
  return res
    ? dedupeHooks(res)
    : res
}

function dedupeHooks (hooks) {
  const res = [];
  for (let i = 0; i < hooks.length; i++) {
    if (res.indexOf(hooks[i]) === -1) {
      res.push(hooks[i]);
    }
  }
  return res
}

LIFECYCLE_HOOKS.forEach(hook => {
  strats[hook] = mergeHook;
});

/**
 * Assets
 *
 * When a vm is present (instance creation), we need to do
 * a three-way merge between constructor options, instance
 * options and parent options.
 */
function mergeAssets (
  parentVal,
  childVal,
  vm,
  key
) {
  const res = Object.create(parentVal || null);
  if (childVal) {
    assertObjectType(key, childVal, vm);
    return extend(res, childVal)
  } else {
    return res
  }
}

ASSET_TYPES.forEach(function (type) {
  strats[type + 's'] = mergeAssets;
});

/**
 * Watchers.
 *
 * Watchers hashes should not overwrite one
 * another, so we merge them as arrays.
 */
strats.watch = function (
  parentVal,
  childVal,
  vm,
  key
) {
  // work around Firefox's Object.prototype.watch...
  if (parentVal === nativeWatch) parentVal = undefined;
  if (childVal === nativeWatch) childVal = undefined;
  /* istanbul ignore if */
  if (!childVal) return Object.create(parentVal || null)
  {
    assertObjectType(key, childVal, vm);
  }
  if (!parentVal) return childVal
  const ret = {};
  extend(ret, parentVal);
  for (const key in childVal) {
    let parent = ret[key];
    const child = childVal[key];
    if (parent && !Array.isArray(parent)) {
      parent = [parent];
    }
    ret[key] = parent
      ? parent.concat(child)
      : Array.isArray(child) ? child : [child];
  }
  return ret
};

/**
 * Other object hashes.
 */
strats.props =
strats.methods =
strats.inject =
strats.computed = function (
  parentVal,
  childVal,
  vm,
  key
) {
  if (childVal && "development" !== 'production') {
    assertObjectType(key, childVal, vm);
  }
  if (!parentVal) return childVal
  const ret = Object.create(null);
  extend(ret, parentVal);
  if (childVal) extend(ret, childVal);
  return ret
};
strats.provide = mergeDataOrFn;

/**
 * Default strategy.
 */
const defaultStrat = function (parentVal, childVal) {
  return childVal === undefined
    ? parentVal
    : childVal
};

/**
 * Validate component names
 */
function checkComponents (options) {
  for (const key in options.components) {
    validateComponentName(key);
  }
}

function validateComponentName (name) {
  if (!new RegExp(`^[a-zA-Z][\\-\\.0-9_${unicodeRegExp.source}]*$`).test(name)) {
    warn(
      'Invalid component name: "' + name + '". Component names ' +
      'should conform to valid custom element name in html5 specification.'
    );
  }
  if (isBuiltInTag(name) || config.isReservedTag(name)) {
    warn(
      'Do not use built-in or reserved HTML elements as component ' +
      'id: ' + name
    );
  }
}

/**
 * Ensure all props option syntax are normalized into the
 * Object-based format.
 */
function normalizeProps (options, vm) {
  const props = options.props;
  if (!props) return
  const res = {};
  let i, val, name;
  if (Array.isArray(props)) {
    i = props.length;
    while (i--) {
      val = props[i];
      if (typeof val === 'string') {
        name = camelize(val);
        res[name] = { type: null };
      } else {
        warn('props must be strings when using array syntax.');
      }
    }
  } else if (isPlainObject(props)) {
    for (const key in props) {
      val = props[key];
      name = camelize(key);
      res[name] = isPlainObject(val)
        ? val
        : { type: val };
    }
  } else {
    warn(
      `Invalid value for option "props": expected an Array or an Object, ` +
      `but got ${toRawType(props)}.`,
      vm
    );
  }
  options.props = res;
}

/**
 * Normalize all injections into Object-based format
 */
function normalizeInject (options, vm) {
  const inject = options.inject;
  if (!inject) return
  const normalized = options.inject = {};
  if (Array.isArray(inject)) {
    for (let i = 0; i < inject.length; i++) {
      normalized[inject[i]] = { from: inject[i] };
    }
  } else if (isPlainObject(inject)) {
    for (const key in inject) {
      const val = inject[key];
      normalized[key] = isPlainObject(val)
        ? extend({ from: key }, val)
        : { from: val };
    }
  } else {
    warn(
      `Invalid value for option "inject": expected an Array or an Object, ` +
      `but got ${toRawType(inject)}.`,
      vm
    );
  }
}

/**
 * Normalize raw function directives into object format.
 */
function normalizeDirectives (options) {
  const dirs = options.directives;
  if (dirs) {
    for (const key in dirs) {
      const def$$1 = dirs[key];
      if (typeof def$$1 === 'function') {
        dirs[key] = { bind: def$$1, update: def$$1 };
      }
    }
  }
}

function assertObjectType (name, value, vm) {
  if (!isPlainObject(value)) {
    warn(
      `Invalid value for option "${name}": expected an Object, ` +
      `but got ${toRawType(value)}.`,
      vm
    );
  }
}

/**
 * Merge two option objects into a new one.
 * Core utility used in both instantiation and inheritance.
 */
function mergeOptions (
  parent,
  child,
  vm
) {
  {
    checkComponents(child);
  }

  if (typeof child === 'function') {
    child = child.options;
  }

  normalizeProps(child, vm);
  normalizeInject(child, vm);
  normalizeDirectives(child);

  // Apply extends and mixins on the child options,
  // but only if it is a raw options object that isn't
  // the result of another mergeOptions call.
  // Only merged options has the _base property.
  if (!child._base) {
    if (child.extends) {
      parent = mergeOptions(parent, child.extends, vm);
    }
    if (child.mixins) {
      for (let i = 0, l = child.mixins.length; i < l; i++) {
        parent = mergeOptions(parent, child.mixins[i], vm);
      }
    }
  }

  const options = {};
  let key;
  for (key in parent) {
    mergeField(key);
  }
  for (key in child) {
    if (!hasOwn(parent, key)) {
      mergeField(key);
    }
  }
  function mergeField (key) {
    const strat = strats[key] || defaultStrat;
    options[key] = strat(parent[key], child[key], vm, key);
  }
  return options
}

/**
 * Resolve an asset.
 * This function is used because child instances need access
 * to assets defined in its ancestor chain.
 */
function resolveAsset (
  options,
  type,
  id,
  warnMissing
) {
  /* istanbul ignore if */
  if (typeof id !== 'string') {
    return
  }
  const assets = options[type];
  // check local registration variations first
  if (hasOwn(assets, id)) return assets[id]
  const camelizedId = camelize(id);
  if (hasOwn(assets, camelizedId)) return assets[camelizedId]
  const PascalCaseId = capitalize(camelizedId);
  if (hasOwn(assets, PascalCaseId)) return assets[PascalCaseId]
  // fallback to prototype chain
  const res = assets[id] || assets[camelizedId] || assets[PascalCaseId];
  if (warnMissing && !res) {
    warn(
      'Failed to resolve ' + type.slice(0, -1) + ': ' + id,
      options
    );
  }
  return res
}

/*  */



function validateProp (
  key,
  propOptions,
  propsData,
  vm
) {
  const prop = propOptions[key];
  const absent = !hasOwn(propsData, key);
  let value = propsData[key];
  // boolean casting
  const booleanIndex = getTypeIndex(Boolean, prop.type);
  if (booleanIndex > -1) {
    if (absent && !hasOwn(prop, 'default')) {
      value = false;
    } else if (value === '' || value === hyphenate(key)) {
      // only cast empty string / same name to boolean if
      // boolean has higher priority
      const stringIndex = getTypeIndex(String, prop.type);
      if (stringIndex < 0 || booleanIndex < stringIndex) {
        value = true;
      }
    }
  }
  // check default value
  if (value === undefined) {
    value = getPropDefaultValue(vm, prop, key);
    // since the default value is a fresh copy,
    // make sure to observe it.
    const prevShouldObserve = shouldObserve;
    toggleObserving(true);
    observe(value);
    toggleObserving(prevShouldObserve);
  }
  {
    assertProp(prop, key, value, vm, absent);
  }
  return value
}

/**
 * Get the default value of a prop.
 */
function getPropDefaultValue (vm, prop, key) {
  // no default, return undefined
  if (!hasOwn(prop, 'default')) {
    return undefined
  }
  const def = prop.default;
  // warn against non-factory defaults for Object & Array
  if (isObject(def)) {
    warn(
      'Invalid default value for prop "' + key + '": ' +
      'Props with type Object/Array must use a factory function ' +
      'to return the default value.',
      vm
    );
  }
  // the raw prop value was also undefined from previous render,
  // return previous default value to avoid unnecessary watcher trigger
  if (vm && vm.$options.propsData &&
    vm.$options.propsData[key] === undefined &&
    vm._props[key] !== undefined
  ) {
    return vm._props[key]
  }
  // call factory function for non-Function types
  // a value is Function if its prototype is function even across different execution context
  return typeof def === 'function' && getType(prop.type) !== 'Function'
    ? def.call(vm)
    : def
}

/**
 * Assert whether a prop is valid.
 */
function assertProp (
  prop,
  name,
  value,
  vm,
  absent
) {
  if (prop.required && absent) {
    warn(
      'Missing required prop: "' + name + '"',
      vm
    );
    return
  }
  if (value == null && !prop.required) {
    return
  }
  let type = prop.type;
  let valid = !type || type === true;
  const expectedTypes = [];
  if (type) {
    if (!Array.isArray(type)) {
      type = [type];
    }
    for (let i = 0; i < type.length && !valid; i++) {
      const assertedType = assertType(value, type[i], vm);
      expectedTypes.push(assertedType.expectedType || '');
      valid = assertedType.valid;
    }
  }

  const haveExpectedTypes = expectedTypes.some(t => t);
  if (!valid && haveExpectedTypes) {
    warn(
      getInvalidTypeMessage(name, value, expectedTypes),
      vm
    );
    return
  }
  const validator = prop.validator;
  if (validator) {
    if (!validator(value)) {
      warn(
        'Invalid prop: custom validator check failed for prop "' + name + '".',
        vm
      );
    }
  }
}

const simpleCheckRE = /^(String|Number|Boolean|Function|Symbol|BigInt)$/;

function assertType (value, type, vm) {
  let valid;
  const expectedType = getType(type);
  if (simpleCheckRE.test(expectedType)) {
    const t = typeof value;
    valid = t === expectedType.toLowerCase();
    // for primitive wrapper objects
    if (!valid && t === 'object') {
      valid = value instanceof type;
    }
  } else if (expectedType === 'Object') {
    valid = isPlainObject(value);
  } else if (expectedType === 'Array') {
    valid = Array.isArray(value);
  } else {
    try {
      valid = value instanceof type;
    } catch (e) {
      warn('Invalid prop type: "' + String(type) + '" is not a constructor', vm);
      valid = false;
    }
  }
  return {
    valid,
    expectedType
  }
}

const functionTypeCheckRE = /^\s*function (\w+)/;

/**
 * Use function string name to check built-in types,
 * because a simple equality check will fail when running
 * across different vms / iframes.
 */
function getType (fn) {
  const match = fn && fn.toString().match(functionTypeCheckRE);
  return match ? match[1] : ''
}

function isSameType (a, b) {
  return getType(a) === getType(b)
}

function getTypeIndex (type, expectedTypes) {
  if (!Array.isArray(expectedTypes)) {
    return isSameType(expectedTypes, type) ? 0 : -1
  }
  for (let i = 0, len = expectedTypes.length; i < len; i++) {
    if (isSameType(expectedTypes[i], type)) {
      return i
    }
  }
  return -1
}

function getInvalidTypeMessage (name, value, expectedTypes) {
  let message = `Invalid prop: type check failed for prop "${name}".` +
    ` Expected ${expectedTypes.map(capitalize).join(', ')}`;
  const expectedType = expectedTypes[0];
  const receivedType = toRawType(value);
  // check if we need to specify expected value
  if (
    expectedTypes.length === 1 &&
    isExplicable(expectedType) &&
    isExplicable(typeof value) &&
    !isBoolean(expectedType, receivedType)
  ) {
    message += ` with value ${styleValue(value, expectedType)}`;
  }
  message += `, got ${receivedType} `;
  // check if we need to specify received value
  if (isExplicable(receivedType)) {
    message += `with value ${styleValue(value, receivedType)}.`;
  }
  return message
}

function styleValue (value, type) {
  if (type === 'String') {
    return `"${value}"`
  } else if (type === 'Number') {
    return `${Number(value)}`
  } else {
    return `${value}`
  }
}

const EXPLICABLE_TYPES = ['string', 'number', 'boolean'];
function isExplicable (value) {
  return EXPLICABLE_TYPES.some(elem => value.toLowerCase() === elem)
}

function isBoolean (...args) {
  return args.some(elem => elem.toLowerCase() === 'boolean')
}

/*  */

function handleError (err, vm, info) {
  // Deactivate deps tracking while processing error handler to avoid possible infinite rendering.
  // See: https://github.com/vuejs/vuex/issues/1505
  pushTarget();
  try {
    if (vm) {
      let cur = vm;
      while ((cur = cur.$parent)) {
        const hooks = cur.$options.errorCaptured;
        if (hooks) {
          for (let i = 0; i < hooks.length; i++) {
            try {
              const capture = hooks[i].call(cur, err, vm, info) === false;
              if (capture) return
            } catch (e) {
              globalHandleError(e, cur, 'errorCaptured hook');
            }
          }
        }
      }
    }
    globalHandleError(err, vm, info);
  } finally {
    popTarget();
  }
}

function invokeWithErrorHandling (
  handler,
  context,
  args,
  vm,
  info
) {
  let res;
  try {
    res = args ? handler.apply(context, args) : handler.call(context);
    if (res && !res._isVue && isPromise(res) && !res._handled) {
      res.catch(e => handleError(e, vm, info + ` (Promise/async)`));
      // issue #9511
      // avoid catch triggering multiple times when nested calls
      res._handled = true;
    }
  } catch (e) {
    handleError(e, vm, info);
  }
  return res
}

function globalHandleError (err, vm, info) {
  if (config.errorHandler) {
    try {
      return config.errorHandler.call(null, err, vm, info)
    } catch (e) {
      // if the user intentionally throws the original error in the handler,
      // do not log it twice
      if (e !== err) {
        logError(e, null, 'config.errorHandler');
      }
    }
  }
  logError(err, vm, info);
}

function logError (err, vm, info) {
  {
    warn(`Error in ${info}: "${err.toString()}"`, vm);
  }
  /* istanbul ignore else */
  if ((inBrowser || inWeex) && typeof console !== 'undefined') {
    console.error(err);
  } else {
    throw err
  }
}

/*  */

let isUsingMicroTask = false;

const callbacks = [];
let pending = false;

function flushCallbacks () {
  pending = false;
  const copies = callbacks.slice(0);
  callbacks.length = 0;
  for (let i = 0; i < copies.length; i++) {
    copies[i]();
  }
}

// Here we have async deferring wrappers using microtasks.
// In 2.5 we used (macro) tasks (in combination with microtasks).
// However, it has subtle problems when state is changed right before repaint
// (e.g. #6813, out-in transitions).
// Also, using (macro) tasks in event handler would cause some weird behaviors
// that cannot be circumvented (e.g. #7109, #7153, #7546, #7834, #8109).
// So we now use microtasks everywhere, again.
// A major drawback of this tradeoff is that there are some scenarios
// where microtasks have too high a priority and fire in between supposedly
// sequential events (e.g. #4521, #6690, which have workarounds)
// or even between bubbling of the same event (#6566).
let timerFunc;

// The nextTick behavior leverages the microtask queue, which can be accessed
// via either native Promise.then or MutationObserver.
// MutationObserver has wider support, however it is seriously bugged in
// UIWebView in iOS >= 9.3.3 when triggered in touch event handlers. It
// completely stops working after triggering a few times... so, if native
// Promise is available, we will use it:
/* istanbul ignore next, $flow-disable-line */
if (typeof Promise !== 'undefined' && isNative(Promise)) {
  const p = Promise.resolve();
  timerFunc = () => {
    p.then(flushCallbacks);
    // In problematic UIWebViews, Promise.then doesn't completely break, but
    // it can get stuck in a weird state where callbacks are pushed into the
    // microtask queue but the queue isn't being flushed, until the browser
    // needs to do some other work, e.g. handle a timer. Therefore we can
    // "force" the microtask queue to be flushed by adding an empty timer.
    if (isIOS) setTimeout(noop);
  };
  isUsingMicroTask = true;
} else if (!isIE && typeof MutationObserver !== 'undefined' && (
  isNative(MutationObserver) ||
  // PhantomJS and iOS 7.x
  MutationObserver.toString() === '[object MutationObserverConstructor]'
)) {
  // Use MutationObserver where native Promise is not available,
  // e.g. PhantomJS, iOS7, Android 4.4
  // (#6466 MutationObserver is unreliable in IE11)
  let counter = 1;
  const observer = new MutationObserver(flushCallbacks);
  const textNode = document.createTextNode(String(counter));
  observer.observe(textNode, {
    characterData: true
  });
  timerFunc = () => {
    counter = (counter + 1) % 2;
    textNode.data = String(counter);
  };
  isUsingMicroTask = true;
} else if (typeof setImmediate !== 'undefined' && isNative(setImmediate)) {
  // Fallback to setImmediate.
  // Technically it leverages the (macro) task queue,
  // but it is still a better choice than setTimeout.
  timerFunc = () => {
    setImmediate(flushCallbacks);
  };
} else {
  // Fallback to setTimeout.
  timerFunc = () => {
    setTimeout(flushCallbacks, 0);
  };
}

function nextTick (cb, ctx) {
  let _resolve;
  callbacks.push(() => {
    if (cb) {
      try {
        cb.call(ctx);
      } catch (e) {
        handleError(e, ctx, 'nextTick');
      }
    } else if (_resolve) {
      _resolve(ctx);
    }
  });
  if (!pending) {
    pending = true;
    timerFunc();
  }
  // $flow-disable-line
  if (!cb && typeof Promise !== 'undefined') {
    return new Promise(resolve => {
      _resolve = resolve;
    })
  }
}

/*  */

let mark;
let measure;

{
  const perf = inBrowser && window.performance;
  /* istanbul ignore if */
  if (
    perf &&
    perf.mark &&
    perf.measure &&
    perf.clearMarks &&
    perf.clearMeasures
  ) {
    mark = tag => perf.mark(tag);
    measure = (name, startTag, endTag) => {
      perf.measure(name, startTag, endTag);
      perf.clearMarks(startTag);
      perf.clearMarks(endTag);
      // perf.clearMeasures(name)
    };
  }
}

/* not type checking this file because flow doesn't play well with Proxy */

let initProxy;

{
  const allowedGlobals = makeMap(
    'Infinity,undefined,NaN,isFinite,isNaN,' +
    'parseFloat,parseInt,decodeURI,decodeURIComponent,encodeURI,encodeURIComponent,' +
    'Math,Number,Date,Array,Object,Boolean,String,RegExp,Map,Set,JSON,Intl,BigInt,' +
    'require' // for Webpack/Browserify
  );

  const warnNonPresent = (target, key) => {
    warn(
      `Property or method "${key}" is not defined on the instance but ` +
      'referenced during render. Make sure that this property is reactive, ' +
      'either in the data option, or for class-based components, by ' +
      'initializing the property. ' +
      'See: https://vuejs.org/v2/guide/reactivity.html#Declaring-Reactive-Properties.',
      target
    );
  };

  const warnReservedPrefix = (target, key) => {
    warn(
      `Property "${key}" must be accessed with "$data.${key}" because ` +
      'properties starting with "$" or "_" are not proxied in the Vue instance to ' +
      'prevent conflicts with Vue internals. ' +
      'See: https://vuejs.org/v2/api/#data',
      target
    );
  };

  const hasProxy =
    typeof Proxy !== 'undefined' && isNative(Proxy);

  if (hasProxy) {
    const isBuiltInModifier = makeMap('stop,prevent,self,ctrl,shift,alt,meta,exact');
    config.keyCodes = new Proxy(config.keyCodes, {
      set (target, key, value) {
        if (isBuiltInModifier(key)) {
          warn(`Avoid overwriting built-in modifier in config.keyCodes: .