javascript - 如何使用 'Function.prototype.call'调用未附加到任何对象原型(prototype)的函数

Question

以下代码的输出是undefine has undefinedwheels，而不是Bike has 2wheels。实例化对象是否无法调用未附加到任何对象的原型(prototype)的函数？

var vehicle = function(name, wheels){
	name = "car",
	wheels = 4,
	fuel = "petrol"
}

function drive(name, wheels) {
	console.log(this.name + " has " + this.wheels + " wheels" );
}

var vehicle1 = new vehicle('Bike' , 2);
drive.call(vehicle1); //undefined is driven with undefined wheels 

Answer 1

不幸的是，您的代码几乎所有内容都是不正确的。

首先，“vehicle”函数必须在 this 上设置属性，并且应该使用传入的参数而不是常量:

var vehicle = function(name, wheels) {
    this.name = name,
    this.wheels = wheels,
    this.fuel = "petrol"
}

然后，您的函数“drive”应该不带任何参数:

function drive() {
  console.log(this.name + " is driven with " + this.wheels + " wheels" );
}

要使用您的车辆作为 this 值调用 drive():

var vehicle1 = new vehicle("Bike", 2);
drive.call(vehicle1); 

.call() 的第一个参数将用作被调用函数内 this 的值。