为什么我们不能在 TypeScript 类中定义一个 const 字段，为什么静态只读不起作用？
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Why can't we define a const field in TypeScript class, and why static readonly is not working?
提问by Aditya
I want to use constkeyword in my program.
我想const在我的程序中使用关键字。
export class Constant {
let result : string;
private const CONSTANT = 'constant'; //Error: A class member cannot have the const keyword.
constructor () {}
public doSomething () {
if (condition is true) {
//do the needful
}
else
{
this.result = this.CONSTANT; // NO ERROR
}
}
}
Question1: why the class member does not have the const keyword in typescript?
问题 1：为什么 class 成员在 typescript 中没有 const 关键字？
Question2: When I use
问题2：当我使用
static readonly CONSTANT = 'constant';
and assign it in
并将其分配给
this.result = this.CONSTANT;
it displays error. why so?
它显示错误。为什么这样？
I have followed this post How to implement class constants in typescript?but don't get the answer why typescript is displaying this kind of error with constkeyword.
我已经关注了这篇文章如何在打字稿中实现类常量？但没有得到答案为什么打字稿用const关键字显示这种错误。
回答by Pac0
Question1:why the class member does not have the const keyword in typescript?
问题1：为什么类成员在打字稿中没有const关键字？
By design. Among other reasons, because EcmaScript6 doesn't either.
按设计。除其他原因外，因为 EcmaScript6也没有.
This question is specifically answered here : 'const' keyword in TypeScript
这个问题在这里专门回答：TypeScript中的'const'关键字
Question2:When I use
static readonly CONSTANT = 'constant';and assign it in
this.result = this.CONSTANT;it displays error. why so?
问题2：当我使用
static readonly CONSTANT = 'constant';并将其分配给
this.result = this.CONSTANT;它显示错误。为什么这样？
If you use static, then you can't refer to your variable with this, but with the the name of the class !
如果你使用static，那么你不能用 来引用你的变量this，而是用类的名称！
export class Constant{
let result : string;
static readonly CONSTANT = 'constant';
constructor(){}
public doSomething(){
if( condition is true){
//do the needful
}
else
{
this.result = Constant.CONSTANT;
}
}
}
Why ? Because thisrefers to the instance of the class to which the field / method belongs. For a static variable / method, it doesn't belong to any instance, but to the class itself (quickly simplified)
为什么 ？因为this是指字段/方法所属的类的实例。对于静态变量/方法，它不属于任何实例，而是属于类本身（快速简化）
