How to access keys of javascript objects dynamically in typescript

Question

interface IObj { 
    fname: string;
    lname: string;
}

const obj: IObj = <IObj>{};

const array: string[] = ['fname', 'lname'];

array.forEach((key: string, index: number) => {
    obj[key] = `${index}`; // Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'IObj'.
});

I want to access object keys dynamically. But typescript is not letting me do it. Is there any way to achieve is in typescript.

@Spangle tried cursing it, didn't fix my problem ;) Any other solutions. — Shubham
– Shubham, Commented Nov 29, 2019 at 4:30

kaya3 · Accepted Answer · 2019-11-29 04:30:06Z

3

You declared array as type string[], and key as type string. If you want Typescript to know these strings are actually keys of IObj, then tell it that:

const array: (keyof IObj)[] = ['fname', 'lname'];

array.forEach((key: keyof IObj, index: number) => {
    obj[key] = `${index}`;
});

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answered Nov 29, 2019 at 4:30

kaya3

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3 Comments

CertainPerformance Over a year ago

There's no need to specify types in the forEach callback if you don't want to, TS can infer them just fine

kaya3 Over a year ago

Yes, indeed; I was just directly adapting the code to change string to the more specific type.

Shubham Over a year ago

@kaya3 Thanks for the quick response. Just one more question, Suppose I have one more object obj2 and I want to assign its value to obj. How should I proceed.

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