Javascript (ES6) Set values to plain Object

Question

How to transform the values of Javascript ES6 Set wrapper into a plain Object? Especially: What is the fastest/shortest way to do so?

I am looking for something like the following that applies to Arrays:

const myArray = Array.from(mySet);

I tried in vain:

// mySet variable is Set containing integers {1, 2, 3, ..., n}

Object.assign({}, mySet);
Object.assign({}, mySet.values());
Object.assign({}, mySet.entries());

Finally, I am thinking about creating a new object, iterating over the set and pushing its entries into the new object. I wonder if there is a more elegant way to do so.

What do you want as output ?

Faly
– Faly

2017-10-25 10:29:42 +00:00
Commented Oct 25, 2017 at 10:29 — Faly
– Faly, Commented Oct 25, 2017 at 10:29
const myObject = {1, 2, 3, ..., n};

Samuel
– Samuel

2017-10-25 10:30:04 +00:00
Commented Oct 25, 2017 at 10:30 — Samuel
– Samuel, Commented Oct 25, 2017 at 10:30
But it's not a valid object

Faly
– Faly

2017-10-25 10:30:50 +00:00
Commented Oct 25, 2017 at 10:30 — Faly
– Faly, Commented Oct 25, 2017 at 10:30
Damn. It is true. So I have to stick to array, I suppose.

Samuel
– Samuel

2017-10-25 10:31:36 +00:00
Commented Oct 25, 2017 at 10:31 — Samuel
– Samuel, Commented Oct 25, 2017 at 10:31
Object.assign( {}, [ ...mySet ])

pawel
– pawel

2017-10-25 10:32:16 +00:00
Commented Oct 25, 2017 at 10:32 — pawel
– pawel, Commented Oct 25, 2017 at 10:32

Faly · Accepted Answer · 2017-10-25 10:49:59Z

2

Use ES6 spread syntax:

var mySet = new Set([1, 2, 3]);
var myArray = [ ...mySet];
console.log(myArray);

EDIT: To get an object instead of an array, it should be:

var mySet = new Set([1, 2, 3]);
var obj = {};
[ ...mySet].forEach(el => obj[el] = el);
console.log(obj);

edited Oct 25, 2017 at 10:49

answered Oct 25, 2017 at 10:35

Faly

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4 Comments

pawel Over a year ago

So you have basically reiterated the "I know how to convert Set into Array" part of the question?

Faly Over a year ago

@pawel The object he want is not valid: { 1, 2, 3, 4 }

pawel Over a year ago

Since he asks for an object I'd assume the expected results would be { 1 : 1, 2 : 2, 3 : 3 }

Samuel Over a year ago

It's ok. I will modify my question slightly. Sorry for confusion.

Shawnnosaurus · Accepted Answer · 2020-09-23 10:00:03Z

The problem is that Set returns an Interactor and objects don't technically exist without keys. You would need to assign a key for each value and the simplest way of doing that is to spread it into a new array, so that the index of the array becomes the key.

// returns { "0": 1, "1": 2, "2": 3, ..., "i": n }
{...{}, ...[...mySet]};

// Same as above.
Object.assign({}, Array.from(mySet));

If however, you want the key and value to be the same in the object, you can run a reducer method on the parsed array, with the initial value as the returned object.

const myReducer = (acc, cur) => {
  // You don't need to stringify, if you can ensure it's always numbers.
  acc[JSON.stringify(cur)] = cur;
  return acc;
};

// Returns { "1": 1, "2": 2, "3": 3, ..., "n": n }
Array.from(mySet).reduce(myReducer, {});

// One liner, as per above, just less readable.
[...mySet].reduce((acc, cur) => !(acc[JSON.stringiy(cur)] = cur) || acc, {});

Disclaimer: As Set can have any primitive value, at any location, the keys can get a bit crazy when assigning objects to it.

// Returns { "1": 1, "{\"test1\":1}": { "test1": 1 } }
[...new Set([1, {test1:1}])].reduce(myReducer, {});

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