How can I convert a Set to an Array in TypeScript

Question

How can I convert a Set (eg, {2,4,6}) to an Array [2, 4, 6] in TypeScript without writing a loop explicitly ?

I have tried those following ways, all of them work in JavaScript but none of them work on TypeScript

[...set] // ERR: "Type 'Set<{}>' is not an array type" in typescript

Array.from(set) // ERR: Property 'from' does not exist on type 'ArrayConstructor'

what target are you compiling to? Both Set and Array.from were added in ES6 and are not available when compiling to ES5. If you want to use them you can try using core.js to get polyfils for them. — toskv, Apr 24 '16 at 21:46
@toskv You are right, it worked when I change target option to 'ES6', my current target is 'ES5' — thanhpk, Apr 24 '16 at 21:50
I'm having a possibly related issue now, `Type 'Set' is not an array type or a string type. Use compiler option '--downlevelIteration' to allow iterating of iterators. ts(2569)`. [mayan anger's answer](https://stackoverflow.com/a/48264936/705296) solved it for me. — Joe Sadoski, Feb 03 '22 at 18:22

mayan anger · Answer 1 · 2018-06-11T21:15:08.140

199

You also can do

Array.from(my_set.values());

edited Jun 11 '18 at 21:15

answered Jan 15 '18 at 14:24

mayan anger

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This should be marked as the correct answer – EuberDeveloper Mar 26 '21 at 15:54
Well, somehow this didn't work for me... my Set is made of strings surrounded by { } so i don't know what is wrong – MonneratRJ Apr 06 '22 at 21:14

score 36 · Answer 2 · answered Jul 21 '20 at 11:55

36

if you declare your set this way:

const mySet = new Set<string>();

you will be able to easily use:

let myArray = Array.from( mySet );

answered Jul 21 '20 at 11:55

OhadR

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basarat · Accepted Answer · 2018-01-11T04:26:35.767

27

Fix

Use tsconfig.json with "lib": ["es6"]

More

Google lib option.
I wrote some docs too : https://basarat.gitbooks.io/typescript/content/docs/types/lib.d.ts.html#lib-option

edited Jan 11 '18 at 04:26

answered Apr 25 '16 at 00:00

basarat

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The doc link is invalid. – kberg Dec 02 '21 at 04:32

score 4 · Answer 4 · answered Oct 19 '20 at 17:39

4

or simply

const mySet = new Set<string>();
mySet.add(1);
mySet.add(2);
console.log([...mySet.values()]);

answered Oct 19 '20 at 17:39

WSD

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score 3 · Answer 5 · answered Nov 05 '20 at 12:49

@basarat's answer wasn't sufficient in my case: I couldn't use the spread operator despite having esnext in my lib array.

To correctly enable using the spread operator on sets and other ES2015 iterables, I had to enable the downlevelIteration compiler option.

Here's how to set it via tsconfig.json:

{
  "compilerOptions": {
    "downlevelIteration": true
  }
}

You will find a more detailed explanation of this flag in the TS documentation page about compiler options.

score 0 · Answer 6 · answered Feb 17 '22 at 12:43

Another solution is using the ! post-fix expression operator to assert that its operand is non-null and non-undefined.

You'll find further information in Non-null assertion operator

You can use the spread operator to convert a Set into an Array:

const mySet = new Set(['h','j','l','l']);
console.log([...mySet!])

How can I convert a Set to an Array in TypeScript

6 Answers6

Fix

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