How do I construct a Set with an Array

Question

I am playing with Set in Node.JS v0.11.3 and the --harmony flag. The API works fine, I can add, remove, clear, etc. I have however not been able to initialise a set with an array. I have tried (as prompted by the MDN page)

var mySet = new Set([1, 1, 2]);

How can I convert an array to a set? Is MDN outdated? Has Node.JS simply not implemented the feature?

• GameAlchemist: looking at the code won't tell ?
• Azmisov: For newcomers, node v12 does support this.
• drekka: Cant seem to get this working in Node V4

Answer 1

The v8 implementation of the Set constructor does not yet support the iterator and comparator arguments mentioned in §15.16.1.1 of the current draft of the Harmony specification, and node uses v8 as its JavaScript interpreter.

As a band-aid, you can use the simplesets package.

Answer 2

Works fine in v8 now using an array supplied to a constructor. I'm using node v6.2.0 (v8 version 5.0.71.47).

> let mySet = new Set([1,2,3]);
undefined
> mySet;
Set { 1, 2, 3 }
> for ( let key of mySet ) { console.log(key) }
1
2
3
undefined
> mySet.size
3

Answer 3

From what I have read it is my understanding that the implementation of this is new and experimental. Some things might not work properly. Also I have noted many instances where new features did not behave as expected until after a period of maturing. It would be best to avoid this and simply add them manually if functionally is your goal.

Answer 4

You can try this one:

• https://github.com/PeterScott/simplesets-nodejs

Sample session:

> var sets = require('simplesets')
undefined
> var mySet = new sets.Set([1, 1, 2]);
undefined
> mySet
{ _items: [ 1, 2 ] }
> mySet.size()
2