将对象添加到现有对象数组 - JavaScript

我创建了一个包含 2 个对象的数组，我希望编写一个“添加”函数来动态地将更多人添加到该数组中。

您能解释一下为什么下面的“add”函数没有成功地将对象添加到“contacts”数组中吗？

var bob = {
    firstName: "Bob",
    lastName: "Jones",
    phoneNumber: "(650) 777-7777",
    email: "[email protected] /cdn-cgi/l/email-protection"
};

var mary = {
    firstName: "Mary",
    lastName: "Johnson",
    phoneNumber: "(650) 888-8888",
    email: "[email protected] /cdn-cgi/l/email-protection"
};

var contacts = [bob, mary];
var contactsLength = contacts.length;

function add (firstName, lastName, phoneNumber, email) {
    contacts[contactsLength] = {
        firstName: firstName,
        lastName: lastName,
        phoneNumber: phoneNumber,
        email: email
    };
};


function printPerson(person) {
    console.log(person.firstName + " " + person.lastName);
}

function list() {
    for (var i = 0; i < contactsLength; i++) {
        printPerson(contacts[i]);
    }
}

add("MJ", "Foster", "MJ@gmail", "714-333-5555");

list();

您的代码未按您认为应有的方式工作的原因是由于这一行：

var contactsLength = contacts.length;

在这里，您分配的值contacts.length到变量contactsLength，但此后，contactsLength即使你的大小也不会改变contacts数组变化。

相反，您应该简单地引用该属性contacts.length.

这是您的代码的更正版本：

var bob = {
    firstName: "Bob",
    lastName: "Jones",
    phoneNumber: "(650) 777-7777",
    email: "[email protected] /cdn-cgi/l/email-protection"
};

var mary = {
    firstName: "Mary",
    lastName: "Johnson",
    phoneNumber: "(650) 888-8888",
    email: "[email protected] /cdn-cgi/l/email-protection"
};

var contacts = [bob, mary];

function add (firstName, lastName, phoneNumber, email) {
    contacts[contacts.length] = {
        firstName: firstName,
        lastName: lastName,
        phoneNumber: phoneNumber,
        email: email
    };
};


function printPerson(person) {
    console.log(person.firstName + " " + person.lastName);
}

function list() {
    for (var i = 0; i < contacts.length; i++) {
        printPerson(contacts[i]);
    }
}

add("MJ", "Foster", "MJ@gmail", "714-333-5555");

list();

请注意：使用原生数组方法push()，会做完全相同的事情contacts[contacts.length] = {...}.