JavaScript/NodeJs - 类型错误 : Cannot set property 'validation' of undefined

Question

我想验证用户表单输入，我只是编写了这段代码，但实际上有一个错误我无法修复，我不明白为什么它在这里(错误)。

let User = (data) => {
    this.data = data
    this.errors = []
}
User.prototype.validation = () => {
    if(this.data.username == ""){
        this.errors.push("You must* provide a username")
    }else if(this.data.email == ""){
        this.errors.push("You must* provide the email address for you account")
    }else if(this.data.password == ""){
        this.errors.push("You must* provide the password for your account")
    }
}
User.prototype.register = () => {
    // step #1 validate user data
    this.validation()
    // step #2 only if there are no validation errors
    // then save the user data into a database
}

module.exports = User

以及我得到的错误。

User.prototype.validation = () => {
                          ^

TypeError: Cannot set property 'validation' of undefined
    at Object.<anonymous> (C:\Users\40sherrin\Desktop\application\models\User.js:5:27)
    at Module._compile (internal/modules/cjs/loader.js:689:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
    at Module.load (internal/modules/cjs/loader.js:599:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
    at Function.Module._load (internal/modules/cjs/loader.js:530:3)
    at Module.require (internal/modules/cjs/loader.js:637:17)
    at require (internal/modules/cjs/helpers.js:22:18)
    at Object.<anonymous> (C:\Users\40sherrin\Desktop\application\controllers\userController.js:1:76)
    at Module._compile (internal/modules/cjs/loader.js:689:30)

Answer 1

您不能对 defining a constructor function 使用箭头函数.

An arrow function expression is a syntactically compact alternative to a regular function expression, although without its own bindings to the this, arguments, super, or new.target keywords. Arrow function expressions are ill suited as methods, and they cannot be used as constructors.

原型(prototype)属性的使用

Arrow functions do not have a prototype property.

let User = function (data) {
    this.data = data
    this.errors = []
}
User.prototype.validation = function() {
    if(this.data.username == ""){
        this.errors.push("You must* provide a username")
    }else if(this.data.email == ""){
        this.errors.push("You must* provide the email address for you account")
    }else if(this.data.password == ""){
        this.errors.push("You must* provide the password for your account")
    }
}
User.prototype.register = function() {
    // step #1 validate user data
    this.validation()
    // step #2 only if there are no validation errors
    // then save the user data into a database
}

因此请使用 function 或 ES6 类。

class User {

   constructor(data) {
       this.data = data
       this.errors = []
   }

   validation() {
      // ...
   }

   register() {
      this.validation();
   }
}