如何使用函数实例化空对象中的值

Question

我无法使用函数向空对象添加值：

我正在尝试使用此代码根据随机数生成汽车对象，这些随机数从数组中提取值并将它们添加到空对象中

var makes = ["BMW", "Audi", "Mercedez", "Range Rover", "Lexus"];
var models= ["M Series", "S Series", "AMG", "Explorer", "F Series"];
var years = [2003, 2017, 2018, 1993, 2006];
var colors = ["black", "red", "blue", "silver", "Red"];
var convertibles = [true, false];

var rand1 = Math.floor(Math.random() * makes.length);
var rand2 = Math.floor(Math.random() * models.length);
var rand3 = Math.floor(Math.random() * years.length);
var rand4 = Math.floor(Math.random() * colors.length);
var rand5 = Math.floor(Math.random() * 5) + 1; //using this one to determine passenger
var rand6 = Math.floor(Math.random() * 2); //using this one to determine whether it's a convertible or not

function makeCar(newCar){
    newCar = {
        make: makes[rand1],
        model: models[rand2],
        year: years[rand3],
        color: colors[rand4],
        passengers: rand5,
        convertible: convertibles[rand6],
        mileage: 0
    };

    return newCar;


}

var Beamer = {};

makeCar(Beamer);

console.log(Beamer);

但是，每当我在 Firefox 的 Web 控制台中运行它时，我都会得到：

{}
​
__proto__: {…}

我正在使用教科书 Headstart: javascript，我看到您可以像这样创建一个空对象：

var lookMaNoProps = { };

然后您可以像这样动态添加到所述空对象：

var lookMaNoProps = { }; lookMaNoProps.age = 10;
if (lookMaNoProps.age > 5) {
lookMaNoProps.school = "Elementary";}

​​​​

只是在试图理解为什么我的没有通过或者是我的语法错误时遇到了一点麻烦。

谢谢

Answer 1

您正在将一个对象传递给您的函数，但随后您正在重新分配一个您返回的新对象，然后不再使用。 你应该这样做：

function makeCar(){
    var newCar = {
        make: makes[rand1],
        model: models[rand2],
        year: years[rand3],
        color: colors[rand4],
        passengers: rand5,
        convertible: convertibles[rand6],
        mileage: 0
    };

    return newCar;


}

var Beamer = makeCar();

或者如果你想改变传递的对象：

function makeCar(newCar){
    Object.assign(newCar, {
        make: makes[rand1],
        model: models[rand2],
        year: years[rand3],
        color: colors[rand4],
        passengers: rand5,
        convertible: convertibles[rand6],
        mileage: 0
    });
}

var Beamer = {};

makeCar(Beamer);

Answer 2

函数makeCar(newCar) 返回一个newCar，但您没有将它保存到对象Beamer，所以它保持为空。

var makes = ["BMW", "Audi", "Mercedez", "Range Rover", "Lexus"];
    var models= ["M Series", "S Series", "AMG", "Explorer", "F Series"];
    var years = [2003, 2017, 2018, 1993, 2006];
    var colors = ["black", "red", "blue", "silver", "Red"];
    var convertibles = [true, false];
    
    var rand1 = Math.floor(Math.random() * makes.length);
    var rand2 = Math.floor(Math.random() * models.length);
    var rand3 = Math.floor(Math.random() * years.length);
    var rand4 = Math.floor(Math.random() * colors.length);
    var rand5 = Math.floor(Math.random() * 5) + 1; //using this one to determine passenger
    var rand6 = Math.floor(Math.random() * 2); //using this one to determine whether it's a convertible or not
    
    function makeCar(){
        var newCar = {
            make: makes[rand1],
            model: models[rand2],
            year: years[rand3],
            color: colors[rand4],
            passengers: rand5,
            convertible: convertibles[rand6],
            mileage: 0
        };
    
        return newCar;
    
    
    }
    
    var Beamer = {};
    
    Beamer = makeCar();
    
    console.log(Beamer);