immutable.js get keys from map/hash

Question

I want to retrieve keys() from the following Immutable Map:

var map = Immutable.fromJS({"firstKey": null, "secondKey": null });
console.log(JSON.stringify(map.keys()));

I would expect the output:

["firstKey", "secondKey"]

However this outputs:

{"_type":0,"_stack":{"node":{"ownerID":{},"entries":[["firstKey",null],["secondKey",null]]},"index":0}}

How to do it properly?

JSFiddle link: https://jsfiddle.net/o04btr3j/57/

lumio · Accepted Answer · 2017-09-07T22:30:31.503

48

Although this question got answered a while ago, here is a little update:

ES6 Solution:

const [ ...keys ] = map.keys();

Pre ES6 Solution:

var keys = map.keySeq().toArray();

edited Sep 07 '17 at 22:30

answered Apr 03 '17 at 18:16

lumio

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ES6 is ES2015. Do you mean pre-ES2015? – Druckles Sep 07 '17 at 22:29
Changed. Thanks for mentioning – lumio Sep 07 '17 at 22:31

score 39 · Answer 2 · answered Feb 25 '16 at 11:51

39

This is how ImmutableJS object looks like.

If you want to get:

["firstKey", "secondKey"]

You need to do:

console.log(map.keySeq().toArray())

answered Feb 25 '16 at 11:51

Sagi Medina

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You can also use the generic `toJS()` to convert immutable types back to normal js objects or arrays. – OlliM Feb 25 '16 at 15:48

score 3 · Answer 3 · answered Sep 05 '18 at 09:11

Possibly just answering my own question that lead me here, but I found mapKeys() which will gives you access to keys in a regular loop. It seems a bit more "the right way". (The docs are so vague, who knows!)

eg:

Map({ a: 1, b: 2 }).mapKeys((key, value) => console.log(key, value))
// a 1
// b 2

score 0 · Answer 4 · answered May 10 '19 at 16:08

Best practice with Immutable.js is to use Immutable data structures and minimize conversions to JavaScript types. For this problem we can use keySeq(), which returns a new Seq.Indexed (an ordered indexed list of values) of the keys of this Map. We then can then set a List to those values and assign that List to a variable for use later. Here is an example of how this solution could be implemented:

import { Map, List } from 'immutable';

const exampleMap = Map({ a: 10, b: 20, c: 30 });

const keys = List(exampleMap.keySeq()); // List [ "a", "b", "c" ]

immutable.js get keys from map/hash

4 Answers4