如何使用数组构造Set

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 Is MDN outdated?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?

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