Iterate over set elements
JavascriptEcmascript 6Javascript Problem Overview
I have turned on the Chrome flag for experimental ECMAscript 6 features, one of which is Set
. As I understand, the details of Set
are broadly agreed upon by the spec writers.
I create a set a
and add the string 'Hello'
a = Set();
a.add('Hello');
but how do I iterate over the elements of a
?
for(let i of a) { console.log(i); }
gives "SyntaxError: Illegal let
declaration outside extended mode"
for(var i of a) { console.log(i); }
gives "SyntaxError: Unexpected identifier"
for(var i in a) { console.log(i); }
gives Undefined
Is it possible to iterate over of a set in Chrome 26?
Javascript Solutions
Solution 1 - Javascript
A very easy way is to turn the Set into an Array first:
let a = new Set();
a.add('Hello');
a = Array.from(a);
...and then just use a simple for loop.
Be aware that Array.from
is not supported in IE11.
Solution 2 - Javascript
Upon the spec from MDN, Set
has a values method:
> The values() method returns a new Iterator object that contains the values for each element in the Set object in insertion order.
So, for iterate through the values, I would do:
var s = new Set(['a1', 'a2'])
for (var it = s.values(), val= null; val=it.next().value; ) {
console.log(val);
}
Solution 3 - Javascript
I use the forEach(..);
function. (documentation)
Solution 4 - Javascript
There are two methods you can use. for...of and forEach
let a = new Set();
a.add('Hello');
for(let key of a) console.log(key)
a.forEach(key => console.log(key))
Solution 5 - Javascript
The of
operator doesn't appear to be currently supported in Chrome. It seems that only FireFox versions 13 through 18 support it. It also appears that none of the browsers actually support Set
although the page does say that some of the tests represent existence and not full functionality or coherence. So it might be that Set
is partially implemented in Chrome.
Solution 6 - Javascript
You can also use the spread operator to convert a Set
into an array (an alternative to Array.from(yourSet)
).
const mySet = new Set();
mySet.add('a');
mySet.add('b')
const iterableSet = [...mySet];
// end up with: ['a', 'b']
// use any Array method on `iterableSet`
const lettersPlusSomething = iterableSet.map(letter => letter + ' something');
Solution 7 - Javascript
Even if the syntactic sugar for iteration hasn't been implemented yet, you can probably still use iterators.
http://www.2ality.com/2012/06/for-of-ff13.html explains
> The special method __iterator__
returns an iterator object. Such an object has a method next()
that either returns the next element in the current iteration sequence or throws StopIteration
if there are no more elements.
So you should be able to iterate over the set using
for (var it = mySet.__iterator__();;) {
var element;
try {
element = it.next();
} catch (ex) {
if (ex instanceof StopIteration) {
break;
} else {
throw ex;
}
}
// Do something with element
}
You can also define a functional version of for…of like
function forOf(collection, f) {
// jQuery.each calling convention for f.
var applyToElement = f.bind(/* this */ collection, /* index */ void 0);
for (var it = collection.__iterator__();;) {
var element;
try {
element = it.next();
} catch (ex) {
if (ex instanceof StopIteration) {
break;
} else {
throw ex;
}
}
// jQuery.each return convention.
if (applyToElement(element) === false) { break; }
}
}
Solution 8 - Javascript
A simple functional approach is to just use forEach
const mySet = new Set([1, 2, 3])
mySet.forEach(a => { console.log(a) })
// 1 2 3
Solution 9 - Javascript
this worked for me
mySet.forEach(async(item) =>{
await doSomething(item)
})
Solution 10 - Javascript
let set = new Set();
set.add(1);
set.add(2);
// This will be an array now, now you can loop normally.
console.log([...set]);
Solution 11 - Javascript
@bizi's answer is close but it did not work for me. This worked on Firefox:
var s= new Set([1,2]),
it = s.values();
for (var val= it.next().value; val=it.next().value;) {
console.log("set: "+val);
}