ts declare怎么用

在 TypeScript 中，`declare` 关键字用于声明全局变量、函数、类、接口和命名空间等。它通常用于声明那些已经存在于 JavaScript 代码中，但是 TypeScript 编译器无法识别的实体。

下面是一些 `declare` 的用法示例：

1. 声明全局变量：

declare var myVar: string;

2. 声明全局函数：

declare function myFunc(arg: number): void;

3. 声明全局类：

declare class MyClass {
  constructor(name: string);
  sayHello(): void;
}

4. 声明全局接口：

declare interface MyInterface {
  name: string;
  age: number;
}

5. 声明命名空间：

declare namespace MyNamespace {
  function myFunc(): void;
  let myVar: number;
}

通过使用 `declare` 关键字，可以让 TypeScript 编译器知道这些实体的存在，避免编译时的错误提示。请注意，`declare` 只是用于编译时的类型检查，并不会在运行时引入任何代码。

相关问题

ts declare使用

In TypeScript, the `declare` keyword is used to tell the compiler that a variable, function, class, or namespace already exists and is defined elsewhere. This is useful when you want to use a library or framework that was written in JavaScript, but you want to write your code in TypeScript.

Here are a few examples of how to use `declare` in TypeScript:

1. Declare a global variable:

declare const myVar: string;

This tells TypeScript that `myVar` is a global variable of type `string`, but the variable is not defined in the current file.

2. Declare a function:

declare function myFunc(param: string): number;

This tells TypeScript that `myFunc` is a function that takes a parameter of type `string` and returns a value of type `number`, but the function is not defined in the current file.

3. Declare a class:

declare class MyClass {
  constructor(param: string);
  myMethod(): void;
}

This tells TypeScript that `MyClass` is a class with a constructor that takes a parameter of type `string`, and the class has a method called `myMethod` that returns `void`, but the class is not defined in the current file.

4. Declare a namespace:

declare namespace MyNamespace {
  const myVar: string;
  function myFunc(param: string): number;
  class MyClass {
    constructor(param: string);
    myMethod(): void;
  }
}

This tells TypeScript that `MyNamespace` is a namespace that contains a variable called `myVar`, a function called `myFunc`, and a class called `MyClass`, but the namespace is not defined in the current file.

Using `declare` in TypeScript is a powerful tool for working with existing JavaScript code and libraries.

ts declare

TypeScript `declare` keyword is used to tell the compiler that a variable, function, or class is defined externally and will be available at runtime. It is typically used when you want to use code written in JavaScript or other libraries that do not have type definitions in TypeScript. By using `declare`, you can inform the compiler about the shape and type of the external code without actually implementing it in TypeScript.

For example, if you have a JavaScript library called "myLibrary" that defines a global variable called "myGlobalVar", you can use `declare` to inform TypeScript about its existence:

declare var myGlobalVar: string;

This tells TypeScript that `myGlobalVar` will be available at runtime and has the type `string`. You can then use `myGlobalVar` in your TypeScript code without any compilation errors.

Similarly, you can use `declare` with functions, classes, modules, or namespaces to provide type information for external code.

Note that `declare` only provides type information and does not emit any JavaScript code during the compilation process. It is mainly used for static type checking purposes.