如何解决TypeError：无法读取简单节点项目中未定义的属性推送？

Question

我正在尝试创建一个简单的地址簿，

//globol object for contacts database
// Business Logic for AddressBook ---------
function AddressBook(contacts) {
    this.contacts = [];
}

AddressBook.prototype.addContact = (contact) => {
    this.contacts.push(contact);
}

// Business Logic for Contacts ---------
function Contact(firstName, lastName, phoneNumber) {
    this.firstName = firstName,
        this.lastName = lastName,
        this.phoneNumber = phoneNumber
}

Contact.prototype.fullName = () => {
    return this.firstName + " " + this.lastName;
}

var addressBook = new AddressBook();
var contact = new Contact("Ada", "Lovelace", "503-555-0100");
var contact2 = new Contact("Grace", "Hopper", "503-555-0199");
addressBook.addContact(contact);
addressBook.addContact(contact2);

console.log(addressBook.contacts);

但它会打印错误

.../通讯录。js:8这个。联络。推（接触）^

TypeError:无法读取地址簿上未定义的属性“push”。在对象上添加联系人（/home/maku/Documents/epicodus/addressBook.js:8:19）。（/home/maku/Documents/epicodus/addressBook.js:25:13）在模块中_在对象处编译（internal/modules/cjs/loader.js:701:30）。模块_扩展。。模块处的js（internal/modules/cjs/loader.js:712:10）。在函数tryModuleLoad（internal/modules/cjs/loader.js:600:32）处加载（internal/modules/cjs/loader.js:539:12）。模块_在函数处加载（内部/modules/cjs/loader.js:531:3）。单元在bootstrapNodeJSCore（internal/bootstrap/node.js:622）启动时运行main（internal/modules/cjs/loader.js:754:12）（internal/bootstrap/node.js:283:19）

Answer 1

arrow函数更改“this”关键字的范围，在addContact方法中，将该方法更改为函数声明，它将删除错误

Answer 2

不要使用箭头功能检查此项

如果使用箭头函数，此将不会绑定到当前实例。您需要使用关键字function创建函数：

function AddressBook(contacts) {
    this.contacts = [];
}

AddressBook.prototype.addContact = function(contact) {
    this.contacts.push(contact);
}

// Business Logic for Contacts ---------
function Contact(firstName, lastName, phoneNumber) {
    this.firstName = firstName,
        this.lastName = lastName,
        this.phoneNumber = phoneNumber
}

Contact.prototype.fullName = function() {
    return this.firstName + " " + this.lastName;
}

var addressBook = new AddressBook();
var contact = new Contact("Ada", "Lovelace", "503-555-0100");
var contact2 = new Contact("Grace", "Hopper", "503-555-0199");
addressBook.addContact(contact);
addressBook.addContact(contact2);

console.log(addressBook.contacts);