CODEWITHSUNDEEP
javascriptloopsfor-loopiterator
Sandman
Sandman

Reputation: 2307

Using this for iterator as opposed to for loop

I came across this piece of code in a project I am working on:

var dataSources = **an array of objects**
var _iteratorNormalCompletion = true;
for (var _iterator = dataSources[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true) {
    var dataSource = _step.value;
    ....
}

Firstly, I have never come across anything like this before (didn't even know what to search for to find any reference material). What is the technical term for it and how does it work? Where does _step.value get assigned? What are the differences between this and a for loop?

Secondly, are there any standout benefits of using this style of for over a standard for loop, as to me it just seems an over-complicated way of achieving the same output:

var dataSources = **an array of objects**
for (var i = 0; i < dataSources.length; ++i) {
    var dataSource = dataSources[i];
    ....
}

Upvotes: 0

Views: 36

Answers (1)

Tamas Hegedus
Tamas Hegedus

Reputation: 29936

Your example seems to be a precompiled version of a for..of loop. This code is not meant to be written by hand, instead you could write this:

var dataSources = **an array of objects**;
for (let dataSource of dataSources) {
    ....
}

And compile it to get the form you showed us.

As you can see this syntax is even shorter than a regular for loop, and has the benefits of being able to iterate over any iterable collection. See the iteration protocol.

Upvotes: 2

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