错误 TS2339:类型“Y"上不存在属性“x" [英] error TS2339: Property 'x' does not exist on type 'Y'

问题描述

我不明白为什么这段代码会产生 TypeScript 错误.(不是原代码，有点派生，请忽略例子中的废话):

I don't understand why this code generates TypeScript error. (It's not the original code and is a bit derived, so please ignore the non-sense in the example):

interface Images {
  [key:string]: string;
}

function getMainImageUrl(images: Images): string {
  return images.main;
}

我收到错误(使用 TypeScript 1.7.5):

I'm getting error (using TypeScript 1.7.5):

错误 TS2339:图像"类型上不存在属性main".

error TS2339: Property 'main' does not exist on type 'Images'.

当然我可以在写作时摆脱错误:

Of course I could get rid of the error when writing:

return images["main"];

我不希望使用字符串来访问该属性.我能做什么?

I'd prefer not using string to access the property. What can I do?

推荐答案

如果您希望能够访问 images.main 那么您必须明确定义它:

If you want to be able to access images.main then you must define it explicitly:

interface Images {
    main: string;
    [key:string]: string;
}

function getMainImageUrl(images: Images): string {
    return images.main;
}

您无法使用点表示法访问索引属性，因为打字稿无法知道对象是否具有该属性.
但是，当您专门定义一个属性时，编译器就会知道它是否存在(或不存在)，它是否可选以及类型是什么.

You can not access indexed properties using the dot notation because typescript has no way of knowing whether or not the object has that property.
However, when you specifically define a property then the compiler knows that it's there (or not), whether it's optional or not and what's the type.

你可以有一个地图实例的辅助类，比如:

You can have a helper class for map instances, something like:

class Map<T> {
    private items: { [key: string]: T };

    public constructor() {
        this.items = Object.create(null);
    }

    public set(key: string, value: T): void {
        this.items[key] = value;
    }

    public get(key: string): T {
        return this.items[key];
    }

    public remove(key: string): T {
        let value = this.get(key);
        delete this.items[key];
        return value;
    }
}

function getMainImageUrl(images: Map<string>): string {
    return images.get("main");
}

我实现了类似的东西，我发现它非常有用.

I have something like that implemented, and I find it very useful.

这篇关于错误 TS2339:类型“Y"上不存在属性“x"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！