Order of DOM NodeList returned by getChildNodes()

Question

The DOM method getChildNodes() returns a NodeList of the children of the current Node. Whilst a NodeList is ordered, is the list guaranteed to be in document order?

For example, given <a><b/><c/><d/></a> is a.getChildNodes() guaranteed to return a NodeList with b, c and d in that order?

The javadoc isn't clear on this.

Solution 1

In my experience, yes. The DOM spec isn't any clearer. If you're paranoid, try something like

current = node.firstChild;
while(null != current) {
    ...
    current = current.nextSibling;
}

Solution 2

A document-ordered node list is the behavior in other implementations of the DOM, such as Javascript's or Python's. And a randomly-ordered node list would be utterly useless. I think it's safe to depend on nodes being returned in document order.

Solution 3

My experience is that every time that I have bothered to look it has been in document order. However, I believe that I read somewhere it is not guaranteed to be in document order. I can't find where I read that right now, so take it as hearsay. I think your best bet if you must have them in document order would be to use FirstChild then NextSibling until there are no more sibs.

Comments

[Adrian Mouat]

Well, it is different; there's a text node in the middle!

[Ben]

I seem to as well; it's surprising how quickly people jump on these questions here!

[Adrian Mouat]

Yes, but no-one has been able to answer it definitively! Let me know if you find that reference.

[Šime Vidas]

I'm curious... Why do you write null != foo instead of foo != null? Is that a Java thing? :)

[jbwharris]

@Šime Vidas I think it's actually a C thing, but with Java's C syntax it seemed wise. The idea is that if you make a typo and write 'null = x' when you meant 'null == x', the compiler will complain. 'x = null' being valid, even in a if test statement. And you should then do the same with the other operators for consistence's sake.

[Šime Vidas]

Aha, not a bad idea. Another mechanism is to put your code trough JSLint which will alert on assignments in if headers and other places where assignments are unusual.

[Adrian Mouat]

I don't think you read the question properly. A NodeList is always ordered (regardless of which method returns it). However, is it guaranteed to be in Document order?

[Tim Büthe]

Eclipse has a warning for that too. I would prefer writing ´foo == null´ because it's more natural to read.