lodash的一些方法 _.assign()

lodash这个js库我一般在写前端的组件的视乎用的比较多，一般在处理数组，复制对象的时候用，lodash采用的是js原生的方法经过包装，所以，相对于一些通过奇技淫巧的方法来达到操作数组和对象的js库来说，它的依赖可能会相对少一点。

---

_.assign

以下是它的源码

  /**
   * Performs a
   * [`SameValueZero`](http://ecma-international.org/ecma-262/7.0/#sec-samevaluezero)
   * comparison between two values to determine if they are equivalent.
   *
   * @static
   * @memberOf _
   * @since 4.0.0
   * @category Lang
   * @param {*} value The value to compare.
   * @param {*} other The other value to compare.
   * @returns {boolean} Returns `true` if the values are equivalent, else `false`.
   * @example
   *
   * var object = { 'a': 1 };
   * var other = { 'a': 1 };
   *
   * _.eq(object, object);
   * // => true
   *
   * _.eq(object, other);
   * // => false
   *
   * _.eq('a', 'a');
   * // => true
   *
   * _.eq('a', Object('a'));
   * // => false
   *
   * _.eq(NaN, NaN);
   * // => true
   */
  function eq(value, other) {
    return value === other || (value !== value && other !== other);
  }
//-------------------------------------------------------------
/**
   * Assigns `value` to `key` of `object` if the existing value is not equivalent
   * using [`SameValueZero`](http://ecma-international.org/ecma-262/7.0/#sec-samevaluezero)
   * for equality comparisons.
   *
   * @private
   * @param {Object} object The object to modify.
   * @param {string} key The key of the property to assign.
   * @param {*} value The value to assign.
   */
  function assignValue(object, key, value) {
    var objValue = object[key];
    if (!(hasOwnProperty.call(object, key) && eq(objValue, value)) ||
        (value === undefined && !(key in object))) {
      baseAssignValue(object, key, value);
    }
  }
//-------------------------------------------------
 /**
   * This method is like `_.assignIn` except that it accepts `customizer`
   * which is invoked to produce the assigned values. If `customizer` returns
   * `undefined`, assignment is handled by the method instead. The `customizer`
   * is invoked with five arguments: (objValue, srcValue, key, object, source).
   *
   * **Note:** This method mutates `object`.
   *
   * @static
   * @memberOf _
   * @since 4.0.0
   * @alias extendWith
   * @category Object
   * @param {Object} object The destination object.
   * @param {...Object} sources The source objects.
   * @param {Function} [customizer] The function to customize assigned values.
   * @returns {Object} Returns `object`.
   * @see _.assignWith
   * @example
   *
   * function customizer(objValue, srcValue) {
   *   return _.isUndefined(objValue) ? srcValue : objValue;
   * }
   *
//--------------------------------------------------
  /**
   * The base implementation of `assignValue` and `assignMergeValue` without
   * value checks.
   *
   * @private
   * @param {Object} object The object to modify.
   * @param {string} key The key of the property to assign.
   * @param {*} value The value to assign.
   */
  function baseAssignValue(object, key, value) {
    object[key] = value;
  }
//---------------------------------------------------
  /**
   * Copies properties of `source` to `object`.
   *
   * @private
   * @param {Object} source The object to copy properties from.
   * @param {Array} props The property identifiers to copy.
   * @param {Object} [object={}] The object to copy properties to.
   * @param {Function} [customizer] The function to customize copied values.
   * @returns {Object} Returns `object`.
   */
  function copyObject(source, props, object, customizer) {
    var isNew = !object;
    object || (object = {});

    var index = -1,
        length = props.length;

    while (++index < length) {
      var key = props[index];

      var newValue = customizer
        ? customizer(object[key], source[key], key, object, source)
        : undefined;

      if (newValue === undefined) {
        newValue = source[key];
      }
      if (isNew) {
        baseAssignValue(object, key, newValue);
      } else {
        assignValue(object, key, newValue);
      }
    }
    return object;
  }
//---------------------------------------------------------------
 /**
   * Creates a function like `_.assign`.
   *
   * @private
   * @param {Function} assigner The function to assign values.
   * @returns {Function} Returns the new assigner function.
   */
  function createAssigner(assigner) {
    return baseRest(function(object, sources) {
      var index = -1,
          length = sources.length,
          customizer = length > 1 ? sources[length - 1] : undefined;

      customizer = (assigner.length > 3 && typeof customizer == 'function')
        ? (length--, customizer)
        : undefined;

      object = Object(object);
      while (++index < length) {
        var source = sources[index];
        if (source) {
          assigner(object, source, index, customizer);
        }
      }
      return object;
    });
  }
//---------------------------------------------

   * function Foo() {
   *   this.a = 1;
   * }
   *
   * function Bar() {
   *   this.c = 3;
   * }
   *
   * Foo.prototype.b = 2;
   * Bar.prototype.d = 4;
   *
   * _.assign({ 'a': 0 }, new Foo, new Bar);
   * // => { 'a': 1, 'c': 3 }
   */
  var assign = createAssigner(function(object, source) {
    copyObject(source, nativeKeys(source), object);
  });

参数

• Object object 目标对象
• [sources] (...Object): 源对象
  作用就是将源对象的可枚举字符串属性分配给目标对象。 源对象从左到右开始。 后续来源覆盖以前来源的属性分配。

 * function Foo() {
   *   this.a = 1;
   * }
   *
   * function Bar() {
   *   this.c = 3;
   * }
   *
   * Foo.prototype.b = 2;
   * Bar.prototype.d = 4;
   *
   * _.assign({ 'a': 0 }, new Foo, new Bar);
   * // => { 'a': 1, 'c': 3 }
   */