Question

I was wondering, JavaScript offers a variety of methods to get the first child element from any element, but which is the best? By best, I mean: most cross-browser compatible, fastest, most comprehensive and predictable when it comes to behaviour. A list of methods/properties I use as aliases:

var elem = document.getElementById('container');
var child = elem.children[0];
var child = elem.firstElementChild; // == children[0]

This works for both cases:

var child = elem.childNodes[0]; // or childNodes[1], see below

That’s in case of forms, or <div> iteration. If I might encounter text elements:

var child = elem.childNodes; // treat as NodeList
var child = elem.firstChild;

As far as I can work out, firstChild uses the NodeList from childNodes, and firstElementChild uses children. I’m basing this assumption on the MDN reference:

childNode is a reference to the first child element of the element node, or null if there isn’t one.

I’m guessing that, in terms of speed, the difference, if any, will be next to nothing, since firstElementChild is effectively a reference to children[0], and the children object is already in memory anyway.

What does throw me, is the childNodes object. I’ve used it to take a look at a form, in a table element. While children lists all form elements, childNodes also seems to include whitespace from the HTML code:

console.log(elem.childNodes[0]);
console.log(elem.firstChild);

Both log <TextNode textContent="\n ">

console.log(elem.childNodes[1]);
console.log(elem.children[0]);
console.log(elem.firstElementChild);

All log <input type="text"…>. How come? I’d understand that one object would allow me to work with the “raw” HTML code, while the other sticks to the DOM, but the childNodes element seems to work on both levels.

To get back to my initial question, my guess would be: if I want the most comprehensive object, childNodes is the way to go, but because of its comprehensiveness, it might not be the most predictable in terms of it returning the element I want/expect at any given moment. Cross-browser support might also prove to be a challenge in that case, though I could be wrong.

Could anyone clarify the distinction between the objects at hand? If there is a speed difference, however negligible, I’d like to know, too. If I’m seeing this all wrong, feel free to educate me.

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PS: Please, please, I like JavaScript, so yes, I want to deal with this sort of thing. Answers like “jQuery deals with this for you” are not what I’m looking for, hence no jquery tag.

Answer 1

Sounds like you’re overthinking it. You’ve observed the difference between childNodes and children, which is that childNodes contains all nodes, including text nodes consisting entirely of whitespace, while children is a collection of just the child nodes that are elements. That’s really all there is to it.

There is nothing unpredictable about either collection, although there are a couple of issues to be aware of:

• IE <= 8 do not include white space-only text nodes in childNodes while other browsers do
• IE <= 8 includes comment nodes within children while other browsers only have elements

children, firstElementChild and friends are just conveniences, presenting a filtered view of the DOM restricted to just elements.