merge-left-utils/dist/index.es.js

Merge objects without structure changes

/*
  naive check is input is like Object

  source: https://stackoverflow.com/a/38555871
*/
const isLikeObject = (value) => typeof value === 'object' &&
    value !== null &&
    value.constructor === Object &&
    Object.prototype.toString.call(value) === '[object Object]';
/*
  Function which always return true
*/
const alwaysTrue = () => true;

/**
  Function merge objects {a} and {b} by [keys]
  If key from {b} is not presented in {a} - it does nothing
  If both objects has key - result will get key from {b}
  if value is seems like object - then we run function recursive for value

  keys - which keys will be checked for objects
  a - left
  b - right
  customLogic (a[key], target[key]) : boolean -
    if it returns true - then get value from {b}, else from {a}
*/
function mergeLeftKeys(keys, source, target, customLogic = alwaysTrue) {
    if (!target) {
        return source;
    }
    return keys.reduce((prev, key) => {
        if (Object.prototype.hasOwnProperty.call(target, key) && customLogic(key, source, target)) {
            if (isLikeObject(source[key])) {
                return Object.assign(Object.assign({}, prev), { [key]: mergeLeftKeys(Object.keys(source[key]), source[key], target[key], customLogic) });
            }
            else {
                return Object.assign(Object.assign({}, prev), { [key]: target[key] });
            }
        }
        else {
            return Object.assign(Object.assign({}, prev), { [key]: source[key] });
        }
    }, {});
}

/**
  Shortcut function
  Replace only existing fields in {a} with {b}

  ex: ({ a: 0, b: 0 }, { a: 1, x: 1 }) -> { a: 1, b: 0 }
*/
function mergeLeft(source, target, customLogic = alwaysTrue) {
    return mergeLeftKeys(Object.keys(source), source, target, customLogic);
}

/**
  Shortcut function
  Drops keys listed in {dropKeys} and replace existing fields in {a} with {b}

  ex: (['a'], { a: 0, b: 0 }, { a: 1, x: 1 }) -> { b: 0 }
*/
function mergeLeftDropping(dropKeys, source, target) {
    const replaceableKeys = Object.keys(source).filter((keyOfSource) => dropKeys.indexOf(keyOfSource) === -1);
    return mergeLeftKeys(replaceableKeys, source, target);
}

/**
  Shortcut function
  Replace only existing fields in {a} with {b} skipping {b} keys from {keys}

  ex: (['a'], { a: 0, b: 0 }, { a: 1, b: 1 }) -> { a: 0, b: 1 }
*/
function mergeLeftExcept(skippingKeys, source, target) {
    return mergeLeftKeys(Object.keys(source), source, target, (keyOfSource) => skippingKeys.indexOf(keyOfSource) === -1);
}

/**
  Shortcut function
  Replace only fields from [keys] arg in {a} with {b}

  ex: (['b'], { a: 0, b: 0 }, { a: 1, b: 1 }) -> { a: 0, b: 1 }
*/
function mergeLeftOnly(keys, source, target) {
    return mergeLeft(source, target, (key) => keys.includes(key));
}

/**
  Shortcut function
  Replace only existing fields in {a} with {b}
  When field from {b} is truthy

  ex: ({ a: 0, b: 0 }, { a: 1, x: 1 }) -> { a: 1, b: 0 }
*/
function mergeLeftTruthy(source, target, customLogic = alwaysTrue) {
    return mergeLeftKeys(Object.keys(source), source, target, (key, source, target) => {
        return !!target[key] && customLogic(key, source, target);
    });
}

export { mergeLeft, mergeLeftDropping, mergeLeftExcept, mergeLeftKeys, mergeLeftOnly, mergeLeftTruthy };
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