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Javascript typeof Nodelist

Beware of Javascript’s quirky typeof:

typeof document.getElementsByTagName('p')

This will return 'function', which I did not expect. What is returned is a NodeList, which behaves like an array, identifies itself as a function, but really is neither.

If you want to detect a NodeList you’re better off with feature detection:

var isNodelist = (typeof myvar.length != 'undefined' &&
  typeof myvar.item != 'undefined')

Do note that this makes it probable you’re dealing with a NodeList – but you can’t be sure.

Arjan van der Gaag

Arjan van der Gaag

A thirtysomething software developer, historian and all-round geek. This is his blog about Ruby, Rails, Javascript, Git, CSS, software and the web. Back to all talks and articles?


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