Iterate over object's keys and values in TypeScript

Question

In plain JavaScript we can iterate over object props and values like so:

const values = Object.keys(obj).map(key => obj[key]);

In TypeScript this syntax is wrong because the TS compiler is displaying the following message:

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type Object.

Is there an alternative way not using Map<string, T> to do it and get the value of each key?

I encountered this problem while building an app using React and TS and I have in my state an object which I need to do something like this:

const stateJSX: HTMLParagraphElement[] = Object.keys(obj).map(key => <p>`${key}: ${obj[key]}`<p>);

Christopher Peisert · Accepted Answer · 2021-10-28 16:17:29Z

14

`Object.keys()`

To use Object.keys(), (as indicated in the original question), you can add a typecast indicating that the object is an indexable type:

for (const key of Object.keys(obj)) {
  console.log(`${key}: ${(obj as {[key: string]: string})[key]}`);
}

Or use a typecast on the key:

for (const key of Object.keys(obj)) {
  console.log(`${key}: ${obj[key as keyof typeof obj]}`);
}

`Object.entries()`

Object.entries() may be used without map() as follows:

for (const [key, value] of Object.entries(obj)) {
    console.log(`${key}: ${value}`);
}

edited Oct 28, 2021 at 16:17

answered Oct 28, 2021 at 15:47

Christopher Peisert

24.5k4 gold badges102 silver badges127 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

captain-yossarian from Ukraine · Accepted Answer · 2020-12-19 22:22:28Z

8

You can easily use it with some help of keyof operator:

const test = <T extends Record<string, unknown>>(obj: T) => {
 return (Object.keys(obj) as Array<keyof T>).map(key => obj[key])
}

You should asure TS, that key variable could be used as index for obj argument

answered Dec 19, 2020 at 22:22

captain-yossarian from Ukraine

33.5k5 gold badges41 silver badges78 bronze badges

3 Comments

jcalz Over a year ago

You may want to note that Object.keys() does not return Array<keyof T> automatically because it is not generally safe to do so

captain-yossarian from Ukraine Over a year ago

@jcalz , yes You are right. I have read related github issue. It is better to use with immutable objects. Btw, do you now the better way to use Object.keys with TS? I know, we can do it with typeguards inside map function, but I think it is a bit overhead

dangerginger Over a year ago

This is the only answer that actually discusses how to do this in TypeScript.

Aplet123 · Accepted Answer · 2020-12-19 22:21:26Z

6

Use Object.entries to iterate over both the keys and the values:

Object.entries(obj).map(([key, value]) => `${key}: ${value}`)

answered Dec 19, 2020 at 22:21

Aplet123

35.8k1 gold badge41 silver badges66 bronze badges

Comments

Suraj Rao · Accepted Answer · 2022-02-01 04:49:07Z

4

Use Object.entries

Object.entries(obj).forEach(([key, value]) => console.log(`${key}: ${value}`))

edited Feb 1, 2022 at 4:49

Suraj Rao

29.7k11 gold badges96 silver badges104 bronze badges

answered Feb 1, 2022 at 3:52

Gibin Jose

733 bronze badges

1 Comment

Elikill58 Over a year ago

This answer is really near to this and this

Collectives™ on Stack Overflow

Iterate over object's keys and values in TypeScript

4 Answers 4

`Object.keys()`

`Object.entries()`

Comments

3 Comments

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

3 Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related