如何在TypeScript中声明函数的返回类型 [英] How to declare Return Types for Functions in TypeScript

问题描述

我在这里检查了 https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md ，它是 TypeScript语言规范，但我我看不到如何声明函数的返回类型的事情.

I checked here https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md which is the TypeScript Language Specifications but I couldn't see one thing that how I can declare a return type of the function.

我在下面的代码中显示了我的期望: greet(name:string):字符串{}

I showed what I was expecting in the code below: greet(name:string): string {}

class Greeter {
  greeting: string;
  constructor(message: string) {
    this.greeting = message;
  }
  greet(): string {
    return "Hello, " + this.greeting;
  }
}

我看到我们可以使用(name:string)=>任何，但它们通常在传递回调函数时使用:

I see we can use something (name:string) => any but they are used mostly when passing callback functions around:

function vote(candidate: string, callback: (result: string) => any) {
  // ...
}

推荐答案

您是正确的-这是一个完全正常的示例-您会看到 var result 是隐式的字符串，因为返回类型在 greet()函数上指定.将类型更改为 number ，您将收到警告.

You are correct - here is a fully working example - you'll see that var result is implicitly a string because the return type is specified on the greet() function. Change the type to number and you'll get warnings.

class Greeter {
    greeting: string;
    constructor (message: string) {
        this.greeting = message;
    }
    greet() : string {
        return "Hello, " + this.greeting;
    }
} 

var greeter = new Greeter("Hi");
var result = greeter.greet();

这是数字示例-如果您尝试执行以下操作，则在游乐场编辑器中会看到红色的花形:

Here is the number example - you'll see red squiggles in the playground editor if you try this:

greet() : number {
    return "Hello, " + this.greeting;
}

这篇关于如何在TypeScript中声明函数的返回类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！