How do you check for whether a checkbox is checked or not checked?

I thought this would work:

if ($(this).attr('checked')) {}

but I had to write it this way:

if ($(t开发者_开发知识库his).is(':checked')) {}

Q: Why?

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When you request the attr checked, you are not getting a boolean value:

// this would be correct
if($(this).attr('checked') == 'checked')

// jQuery 1.6+
if($(this).prop('checked'))

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Having been through this recently, it depends on what version of jQuery you are using. As of 1.6, the functioning of attr with native properties (e.g. "checked", "disabled") -- properties being attributes that are supposed to either exist or not - changed, because they could return inconsistent results depending on browser behavior.

The correct way to set or test a property in 1.6 is with the new prop function, which returns true or false always. The 2nd method you use is also valid to test.

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Interesting info about attr and prop jQuery 1.6 and 1.6.1.

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Better yet, just use this.checked, which returns either "true" or "false". No need to use jQuery especially if you already have the DOM node.