Question

我创建了一个JS类。以下是代码：

export default class Service {
    constructor(
        serviceId,
        serviceName,
        serviceDescription,
        serviceImageName,
        categoryId,
        servicePrice,
        currencyCode,
        acceptPayment,
        serviceDuration,
        multipleBookingPerSlot,
        mode,
        tzSupport,
        minOptionCount
    ) {
        try{
            this.id = serviceId;
            this.title = serviceName;
            this.subTitle = serviceDescription;
            this.imageUrl = serviceImageName;
            this.categoryId = categoryId;
            this.price = servicePrice;
            this.currencyCode = currencyCode;
            this.acceptPayment = acceptPayment;
            this.meetingDuration = serviceDuration;
            this.multipleBookingPerSlot = multipleBookingPerSlot;
            this.serviceName = serviceName;
            this.mode = mode;
            this.tzSupport = tzSupport;
            this.session = minOptionCount
        } catch(e){
            if(e instanceof ReferenceError){
                console.error("Service data missing.")
            }
        }

    }
}

我的目标是每当Service的新对象创建类似new Service('1')时，如果任何密钥丢失，代码应该抛出错误并停止执行。我怎样才能做到这一点？

Answer 1

如果来电者没有提供足够的参数，您将无法获得ReferenceError，您只需在参数中看到undefined。

你有13个参数（远远太多）。你可以做蛮力的事情：

if (arguments.length < 13) {
    throw new Error("Missing arguments");
}

相反，我建议使用构建器模式或选项对象而不是13个离散参数。超过三个参数相当难以管理。

例如，使用选项对象：

export default class Service {
    constructor(
        options
    ) {
        ["id", "title", "subTitle", "imageUrl", "categoryId", "price", "currencyCode",
        "acceptPayment", "meetingDuration", "multipleBookingPerSlot", "serviceName",
        "mode", "tzSupport", "session"].forEach(name => {
            if (!options.hasOwnProperty(name)) {
                throw new Error(name + " is a required option");
            }
        });
        Object.assign(this, options);
    }
}

用法：

let s = new Service({id: 1, title: "foo", /*...etc...*/});

这样，来电者就不会在参数范围内迷失。

然而，如果验证参数值是否重要，那么验证其值是否也很重要？没有什么可以阻止我用13个完全无效的参数调用new Service（例如undefined重复13次）。

所以我可能会使用一个options对象（因为它对调用者来说更容易）与参数解构相结合，然后进行单独验证，例如：

export default class Service {
    constructor({                 // <== Notice the {
        id,
        name,
        decription,
        imageUrl,
        categoryId,
        price,
        currencyCode,
        acceptPayment,
        meetingDuration,
        multipleBookingPerSlot,
        mode,
        tzSupport,
        minOptionCount
    }) {                          // <== And the }
        this.id = validate.positiveNumber(id);
        this.title = validate.nonBlank(name);
        this.subTitle = validate.nonBlank(description);
        this.imageUrl = validate.URL(imageUrl);
        this.categoryId = validate.positiveNumber(categoryId);
        this.price = validate.price(price);
        this.currencyCode = validate.currencyCode(currencyCode);
        this.acceptPayment = validate.boolean(acceptPayment);
        this.meetingDuration = validate.duration(meetingDuration);
        this.multipleBookingPerSlot = validate.boolean(multipleBookingPerSlot);
        this.serviceName = this.title; // Already validated
        this.mode = validate.mode(mode);
        this.tzSupport = validate.tzSupport(tzSupport);
        this.session = validate.whateverThisIs(minOptionCount);
    }
}

...其中validate是一组可重复使用的验证。用法与上述相同：

let s = new Service({id: 1, title: "foo", /*...etc...*/});

Answer 2

正如我已经评论过，将undefined赋值给对象属性是完全有效的。解决方案可能是检查Arraylike与undefined的参数值：

constructor(a,b,c){
   if(arguments.length!=3){//check length
     return;
   }
   for(var a=0;a<arguments.length;a++){
      if(arguments[a]===undefined){//check against undefined
          return;
       }
    }
  //your code
}

http://jsbin.com/vugepakama/edit?console

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