函数与构造函数参数验证

函数与构造函数参数验证

• 跟保护和验证对象属性类似，也可对函数和构造函数参数进行审查。比如，可以让函数只接受某种类似的值:

  function median(...nums) {
    return nums.sort()[Math.floor(nums.length / 2)];
  }
  const proxy = new Proxy(median, {
    apply(target, thisArg, argumentsList) {
      for (const arg of argumentsList) {
        if (typeof arg !== "number") {
          throw "Non-number argument provided";
        }
      }
      return Reflect.apply(...arguments);
    },
  });
  console.log(proxy(4, 7, 1)); // 4
  console.log(proxy(4, "7", 1));
  // Error: Non-number argument provided
  

• 类似地，可以要求实例化时必须给构造函数传参

  class User {
    constructor(id) {
      this._id = id;
    }
  }
  const proxy = new Proxy(User, {
    construct(target, argumentsList, newTarget) {
      if (argumentsList[0] === undefined) {
        throw "User cannot be instantiated without id";
      } else {
        return Reflect.construct(...arguments);
      }
    },
  });
  
  new proxy(1);
  
  new proxy();
  // Error: User cannot be instantiated without id