为什么函数 getVehicleName 在车辆对象中打印全局变量车辆名称而不是变量车辆名称

Question

>我在全局范围内以及车辆对象内部声明了一个 vehicleName 变量，在全局范围内声明了一个 printVehicleName 并在 Vehicle 对象内声明了 getVehicleName。当我调用这两个函数时，两者都打印在全局范围内声明的车辆名称。为什么会这样？

//declaring a global variable
let vehicleName = "Dodge";
//declaring  a method to print vehicleName
function printVehicleName(){
    console.log(vehicleName);
}
//declaring a object using object literal notation
let Vehicle = {
    vehicleName : "Ferrari",
    getVehicleName : printVehicleName
};
//executing printVehicleName function
printVehicleName();
//executing getVehicleName function
Vehicle.getVehicleName();

我希望 getVehicleName 函数打印"法拉利"，但是当我调用这两个函数时，两者都会打印在全局范围"闪避"上声明的车辆名称。谁能解释一下这样做的原因以及打印"Ferrai"的方法？

Answer 1

以下是

你得到道奇的原因。

1. printVehicleName()将始终引用全局变量(即使它被分配给对象中的方法(

2. Vehicle.getVehicleName()与printVehicleName()相同

   //declaring a global variable
   let vehicleName = "Dodge";
   //declaring  a method to print vehicleName
   function printVehicleName(){
       console.log(vehicleName); // vehicleName is global variable
   }
   //declaring a object using object literal notation
   let Vehicle = {
       vehicleName : "Ferrari",
       getVehicleName : printVehicleName // Referring to the global function
   };
   //executing printVehicleName function
   printVehicleName();
   //executing getVehicleName function
   Vehicle.getVehicleName(); // This is == to printVehicleName()
   

若要使 Vehicle 对象打印自己的变量，需要使用this变量。

简而言之，您不能对对象中的方法重用printVehicleName，因为如果您打印this.vehicleName，它将不再正常工作。

您需要在对象中采用不同的方法，如下所示。

    let Vehicle = {
        vehicleName: "Ferrari",
        getVehicleName: function() { console.log(this.vehicleName); }
    };

Answer 2

在你的函数中使用关键字this。

this.vehicleName

使用此选项可访问对象属性。

Answer 3

您需要

实际创建一个method并使用this将上下文设置为Vehicle对象内的vehicleName。

对象可以在创建之前引用其 self 属性

let vehicleName = "Dodge";
//declaring  a method to print vehicleName
function printVehicleName() {
  console.log(vehicleName);
}
//declaring a object using object literal notation
let Vehicle = {
  vehicleName: "Ferrari",
  getVehicleName: function() {
    return this.vehicleName
  }
};
//executing printVehicleName function
printVehicleName();
//executing getVehicleName function
console.log(Vehicle.getVehicleName());

您可以重复使用printVehicleName .此行printVehicleName(vcName = vehicleName)将采用默认vehicleName但是从getVehicleName调用时，您可以传递上下文

//declaring a global variable
let vehicleName = "Dodge";
//declaring  a method to print vehicleName
function printVehicleName(vcName = vehicleName) {
  return vcName;
}
//declaring a object using object literal notation
let Vehicle = {
  vehicleName: "Ferrari",
  getVehicleName: function() {
    return printVehicleName(this.vehicleName)
  }
};
//executing printVehicleName function
printVehicleName();
//executing getVehicleName function
console.log(Vehicle.getVehicleName());

Answer 4

我更改了车辆声明部分首先更改车辆名称的值，然后调用 printVehicleName 函数

 let vehicleName = "Dodge";
        //declaring  a method to print vehicleName
        function printVehicleName( ) {
     
            console.log(vehicleName);
           
        }
 
        //declaring a object using object literal notation
        let Vehicle = {
            vehicleName:"Ferrari",
            getVehicleName: function () { vehicleName = this.vehicleName; printVehicleName() }
        };
 
  
        //executing printVehicleName function
       
        printVehicleName(vehicleName);
        //executing getVehicleName function
        Vehicle.getVehicleName();