使用打字稿中的变量访问对象键 [英] Access object key using variable in typescript

问题描述

在打字稿中，如何使用变量访问对象键(属性)?

In typescript, How to access object key(property) using variable?

例如:

interface Obj {
    a: Function;
    b: string;
}

let obj: Obj = {
    a: function() { return 'aaa'; },
    b: 'bbbb'
}

for(let key in obj) {
    console.log(obj[key]);
}

但打字稿会抛出以下错误消息:

but typescript throw below error message:

'TS7017 元素隐式具有 'any' 类型，因为类型 'obj' 没有索引签名'

'TS7017 Element implicitly has an 'any' type because type 'obj' has no index signature'

如何解决?

推荐答案

要使用 --noImplicitAny 编译此代码，您需要具有某种类型检查版本的 Object.keys(obj) 函数，在某种意义上进行了类型检查，已知它仅返回 obj 中定义的属性名称.

To compile this code with --noImplicitAny, you need to have some kind of type-checked version of Object.keys(obj) function, type-checked in a sense that it's known to return only the names of properties defined in obj.

TypeScript AFAIK 中没有内置这样的函数，但您可以提供自己的:

There is no such function built-in in TypeScript AFAIK, but you can provide your own:

interface Obj {
    a: Function;
    b: string;
}

let obj: Obj = {
    a: function() { return 'aaa'; },
    b: 'bbbb'
};


function typedKeys<T>(o: T): (keyof T)[] {
    // type cast should be safe because that's what really Object.keys() does
    return Object.keys(o) as (keyof T)[];
}


// type-checked dynamic property access
typedKeys(obj).forEach(k => console.log(obj[k]));

// verify that it's indeed typechecked
typedKeys(obj).forEach(k => {
    let a: string = obj[k]; //  error TS2322: Type 'string | Function' 
                           // is not assignable to type 'string'.
                          //  Type 'Function' is not assignable to type 'string'.
});

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