mixpanel-browser/src/promise-polyfill.js

The official Mixpanel JavaScript browser client library

import { window } from './window';
/**
 * Promise polyfill sourced from https://github.com/getify/native-promise-only.
 * Modified to
 *  - remove UMD wrapper and export as an object, so that we don't globally polyfill Promise.
 *  - rename access notation for dynamically referenced props to avoid minification, e.g. this.__NPO__ -> this['__NPO__']
*/

/*! Native Promise Only
    v0.8.1 (c) Kyle Simpson
    MIT License: http://getify.mit-license.org
*/

/*jshint validthis:true */
'use strict';

var setImmediate = window['setImmediate'];
var builtInProp, cycle, schedulingQueue,
    ToString = Object.prototype.toString,
    timer = (typeof setImmediate !== 'undefined') ?
        function timer(fn) { return setImmediate(fn); } :
        setTimeout;

// dammit, IE8.
try {
    Object.defineProperty({},'x',{});
    builtInProp = function builtInProp(obj,name,val,config) {
        return Object.defineProperty(obj,name,{
            value: val,
            writable: true,
            configurable: config !== false
        });
    };
}
catch (err) {
    builtInProp = function builtInProp(obj,name,val) {
        obj[name] = val;
        return obj;
    };
}

// Note: using a queue instead of array for efficiency
schedulingQueue = (function Queue() {
    var first, last, item;

    function Item(fn,self) {
        this.fn = fn;
        this.self = self;
        this.next = void 0;
    }

    return {
        add: function add(fn,self) {
            item = new Item(fn,self);
            if (last) {
                last.next = item;
            }
            else {
                first = item;
            }
            last = item;
            item = void 0;
        },
        drain: function drain() {
            var f = first;
            first = last = cycle = void 0;

            while (f) {
                f.fn.call(f.self);
                f = f.next;
            }
        }
    };
})();

function schedule(fn,self) {
    schedulingQueue.add(fn,self);
    if (!cycle) {
        cycle = timer(schedulingQueue.drain);
    }
}

// promise duck typing
function isThenable(o) {
    var _then, oType = typeof o;

    if (o !== null && (oType === 'object' || oType === 'function')) {
        _then = o.then;
    }
    return typeof _then === 'function' ? _then : false;
}

function notify() {
    for (var i=0; i<this.chain.length; i++) {
        notifyIsolated(
            this,
            (this.state === 1) ? this.chain[i].success : this.chain[i].failure,
            this.chain[i]
        );
    }
    this.chain.length = 0;
}

// NOTE: This is a separate function to isolate
// the `try..catch` so that other code can be
// optimized better
function notifyIsolated(self,cb,chain) {
    var ret, _then;
    try {
        if (cb === false) {
            chain.reject(self.msg);
        }
        else {
            if (cb === true) {
                ret = self.msg;
            }
            else {
                ret = cb.call(void 0,self.msg);
            }

            if (ret === chain.promise) {
                chain.reject(TypeError('Promise-chain cycle'));
            }
            // eslint-disable-next-line no-cond-assign
            else if (_then = isThenable(ret)) {
                _then.call(ret,chain.resolve,chain.reject);
            }
            else {
                chain.resolve(ret);
            }
        }
    }
    catch (err) {
        chain.reject(err);
    }
}

function resolve(msg) {
    var _then, self = this;

    // already triggered?
    if (self.triggered) { return; }

    self.triggered = true;

    // unwrap
    if (self.def) {
        self = self.def;
    }

    try {
        // eslint-disable-next-line no-cond-assign
        if (_then = isThenable(msg)) {
            schedule(function(){
                var defWrapper = new MakeDefWrapper(self);
                try {
                    _then.call(msg,
                        function $resolve$(){ resolve.apply(defWrapper,arguments); },
                        function $reject$(){ reject.apply(defWrapper,arguments); }
                    );
                }
                catch (err) {
                    reject.call(defWrapper,err);
                }
            });
        }
        else {
            self.msg = msg;
            self.state = 1;
            if (self.chain.length > 0) {
                schedule(notify,self);
            }
        }
    }
    catch (err) {
        reject.call(new MakeDefWrapper(self),err);
    }
}

function reject(msg) {
    var self = this;

    // already triggered?
    if (self.triggered) { return; }

    self.triggered = true;

    // unwrap
    if (self.def) {
        self = self.def;
    }

    self.msg = msg;
    self.state = 2;
    if (self.chain.length > 0) {
        schedule(notify,self);
    }
}

function iteratePromises(Constructor,arr,resolver,rejecter) {
    for (var idx=0; idx<arr.length; idx++) {
        (function IIFE(idx){
            Constructor.resolve(arr[idx])
                .then(
                    function $resolver$(msg){
                        resolver(idx,msg);
                    },
                    rejecter
                );
        })(idx);
    }
}

function MakeDefWrapper(self) {
    this.def = self;
    this.triggered = false;
}

function MakeDef(self) {
    this.promise = self;
    this.state = 0;
    this.triggered = false;
    this.chain = [];
    this.msg = void 0;
}

function NpoPromise(executor) {
    if (typeof executor !== 'function') {
        throw TypeError('Not a function');
    }

    if (this['__NPO__'] !== 0) {
        throw TypeError('Not a promise');
    }

    // instance shadowing the inherited "brand"
    // to signal an already "initialized" promise
    this['__NPO__'] = 1;

    var def = new MakeDef(this);

    this['then'] = function then(success,failure) {
        var o = {
            success: typeof success === 'function' ? success : true,
            failure: typeof failure === 'function' ? failure : false
        };
            // Note: `then(..)` itself can be borrowed to be used against
            // a different promise constructor for making the chained promise,
            // by substituting a different `this` binding.
        o.promise = new this.constructor(function extractChain(resolve,reject) {
            if (typeof resolve !== 'function' || typeof reject !== 'function') {
                throw TypeError('Not a function');
            }

            o.resolve = resolve;
            o.reject = reject;
        });
        def.chain.push(o);

        if (def.state !== 0) {
            schedule(notify,def);
        }

        return o.promise;
    };
    this['catch'] = function $catch$(failure) {
        return this.then(void 0,failure);
    };

    try {
        executor.call(
            void 0,
            function publicResolve(msg){
                resolve.call(def,msg);
            },
            function publicReject(msg) {
                reject.call(def,msg);
            }
        );
    }
    catch (err) {
        reject.call(def,err);
    }
}

var PromisePrototype = builtInProp({},'constructor',NpoPromise,
    /*configurable=*/false
);

    // Note: Android 4 cannot use `Object.defineProperty(..)` here
NpoPromise.prototype = PromisePrototype;

// built-in "brand" to signal an "uninitialized" promise
builtInProp(PromisePrototype,'__NPO__',0,
    /*configurable=*/false
);

builtInProp(NpoPromise,'resolve',function Promise$resolve(msg) {
    var Constructor = this;

    // spec mandated checks
    // note: best "isPromise" check that's practical for now
    if (msg && typeof msg === 'object' && msg['__NPO__'] === 1) {
        return msg;
    }

    return new Constructor(function executor(resolve,reject){
        if (typeof resolve !== 'function' || typeof reject !== 'function') {
            throw TypeError('Not a function');
        }

        resolve(msg);
    });
});

builtInProp(NpoPromise,'reject',function Promise$reject(msg) {
    return new this(function executor(resolve,reject){
        if (typeof resolve !== 'function' || typeof reject !== 'function') {
            throw TypeError('Not a function');
        }

        reject(msg);
    });
});

builtInProp(NpoPromise,'all',function Promise$all(arr) {
    var Constructor = this;

    // spec mandated checks
    if (ToString.call(arr) !== '[object Array]') {
        return Constructor.reject(TypeError('Not an array'));
    }
    if (arr.length === 0) {
        return Constructor.resolve([]);
    }

    return new Constructor(function executor(resolve,reject){
        if (typeof resolve !== 'function' || typeof reject !== 'function') {
            throw TypeError('Not a function');
        }

        var len = arr.length, msgs = Array(len), count = 0;

        iteratePromises(Constructor,arr,function resolver(idx,msg) {
            msgs[idx] = msg;
            if (++count === len) {
                resolve(msgs);
            }
        },reject);
    });
});

builtInProp(NpoPromise,'race',function Promise$race(arr) {
    var Constructor = this;

    // spec mandated checks
    if (ToString.call(arr) !== '[object Array]') {
        return Constructor.reject(TypeError('Not an array'));
    }

    return new Constructor(function executor(resolve,reject){
        if (typeof resolve !== 'function' || typeof reject !== 'function') {
            throw TypeError('Not a function');
        }

        iteratePromises(Constructor,arr,function resolver(idx,msg){
            resolve(msg);
        },reject);
    });
});

var PromisePolyfill;
if (typeof Promise !== 'undefined' && Promise.toString().indexOf('[native code]') !== -1) {
    PromisePolyfill = Promise;
} else {
    PromisePolyfill = NpoPromise;
}

export { PromisePolyfill as Promise, NpoPromise };