Angular 7 为基元添加扩展方法

问题描述：

我想为基元添加一些方法.我有以下文件:

I would like to add few methods to primitives. I have the following file:

string-extension.ts:

interface String {
    isNullOrEmpty(this: string): boolean;
}

String.prototype.isNullOrEmpty = function (this: string): boolean {
    return !this;
};

我有一个包含以下代码的组件:

I have a component which has the following code:

constructor () {
    let a = "asd";
    alert(a.isNullOrEmpty());
}

顶部没有添加导入.当我运行客户端时，它在那条线上崩溃了.

no import is added at the top. When I run the client, it crashes on that line.

a.isNullOrEmpty is not a function

当我检查代码时，我发现我的 string-extension.ts 文件没有包含在那里.我非常熟悉 C# 中的概念，但我对 TypeScript 中的概念不太熟悉，所以如果您需要更多信息，请提供.

When I inspect the code, i see that my string-extension.ts file wasn't included there. I am very familiar with the concept in C# but im not quite familiar with it in TypeScript, so if you need more info, ill provide.

谢谢.

答

首先，创建global .d.ts.文件来设置签名.

first, create global .d.ts. file to set up the signature.

global.d.ts.

export {}; // this file needs to be a module
declare global {
  interface String {
        isNullOrEmpty(this: string): boolean;
  }
}

string-extension.ts:

export {}; // this file needs to be a module
String.prototype.isNullOrEmpty = function (this: string): boolean {
    return !this;
};

现在在 main.ts 中导入扩展

 import './string-extension'

Angular 7 为基元添加扩展方法

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