code: function (target) {
    if (target) {
      var args = arguments
      if (target === true) {
        if (args.length > 1) {
          target = isArray(target[1]) ? [] : {}
          return extend(target, args, true)
        }
      } else {
        return objectAssignFns ? objectAssignFns.apply(Object, args) : extend(target, args)
      }
    }
    return target
  }
docs: 浅拷贝一个或者多个对象到目标对象中
  
  @param {Object} obj 目标对象
  @param {...Object}
  @return {Boolean}