code: function forEach(array, itemCallback) {
    for (let i = 0, len = array.length; i < len; i++) {
      if (itemCallback) {
        itemCallback.call(array[i], array[i], i);
      }
    }
  }
docs: 对数组进行遍历
  @access private
  @param {Array} array
  @param {Function} itemCallback:function(value,index){}