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When is null or undefined used in JavaScript?

rated 0 times [ 14] [ 2] / answers: 1 / hits: 115653 / 13 Years ago, tue, june 21, 2011, 12:00:00

I am really confused as to when JavaScript returns null or undefined. Also different browsers seem to be returning these differently.

Could you please give some examples of null/undefined with the browsers that return them.

While I am now clear on the undefined aspect, I am still not 100% clear on null. Is it similar to a blank value?

E.g. You have a text box which does not have any value set. Now when you try to access its value, will it be null or undefined and are they similar?

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bryonk

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answered 13 Years ago leannjaidynd · Accepted Answer

The DOM methods getElementById(), nextSibling(), childNodes[n], parentNode() and so on return null (defined but having no value) when the call does not return a node object.

The property is defined, but the object it refers to does not exist.

This is one of the few times you may not want to test for equality-

if(x!==undefined) will be true for a null value

but if(x!= undefined) will be true (only) for values that are not either undefined or null.