_.filter(collection, [predicate=_.identity])

69

_.filter(collection, [predicate=_.identity])

_.filter和原生的filter方法类似，遍历数组，将predicate处理后结果为真值的元素组成一个新数组返回

参数

collection (Array|Object): 需要遍历的集合
[predicate=_.identity] (Function):每一次遍历调用的方法

返回值

(Array): 返回过滤后的新数组

例子

var users = [
  { 'user': 'barney', 'age': 36, 'active': true },
  { 'user': 'fred',   'age': 40, 'active': false }
];
 
_.filter(users, function(o) { return !o.active; });
// => objects for ['fred']
 
// The `_.matches` iteratee shorthand.
_.filter(users, { 'age': 36, 'active': true });
// => objects for ['barney']
 
// The `_.matchesProperty` iteratee shorthand.
_.filter(users, ['active', false]);
// => objects for ['fred']
 
// The `_.property` iteratee shorthand.
_.filter(users, 'active');
// => objects for ['barney']

源代码：

省略iteratee的处理，想看iteratee的处理看这里，https://www.cnblogs.com/hahazexia/p/9901435.html

/**
 * Iterates over elements of `array`, returning an array of all elements
 * `predicate` returns truthy for. The predicate is invoked with three
 * arguments: (value, index, array).
 *
 * **Note:** Unlike `remove`, this method returns a new array.
 *
 * @since 5.0.0
 * @category Array
 * @param {Array} array The array to iterate over.
 * @param {Function} predicate The function invoked per iteration.
 * @returns {Array} Returns the new filtered array.
 * @see pull, pullAll, pullAllBy, pullAllWith, pullAt, remove, reject
 * @example
 *
 * const users = [
 *   { 'user': 'barney', 'active': true },
 *   { 'user': 'fred',   'active': false }
 * ]
 *
 * filter(users, ({ active }) => active)
 * // => objects for ['barney']
 */
//和原生的filter方法类似，遍历数组，将predicate处理后结果为真值的元素组成一个新数组返回
function filter(array, predicate) {
  let index = -1//循环索引
  let resIndex = 0
  const length = array == null ? 0 : array.length//数组长度
  const result = []//结果数组

  while (++index < length) {
    const value = array[index]
    if (predicate(value, index, array)) {//如果predicate返回true，就把当前元素加入结果数组
      result[resIndex++] = value
    }
  }
  return result
}

export default filter