Should setting `checkbox.checked = false` not clear the HTML attribute too?

Question

Here's my HTML:

<input id="test" type="checkbox" checked="">

Here's a Firebug excerpt:

>>> test
<input id="test" type="checkbox" checked="">

>>> test.checked = false
false

>>> test
<input id="test" type="checkbox" checked="">

Um...am I missing something, or should that last line not read the following?

<input id="test" type="checkbox">

UI-wise, the checkbox does indeed uncheck when I execute the checked = false line.

Anyway, if there's some legitimate explanation for this, then what's the proper way to uncheck a checkbox from JavaScript, if not checked = false?

Ferrule

You probably should not care what Firebug says as long as the data gets to your server and the UI behaves as expected. – Fix

This is just to demonstrate what I'm talking about. The real problem is that I have CSS that I want to have an effect based on whether the checkbox is checked or not, and it only does its job when I click the checkbox, not when I set .checked. – Ferrule

Answer 1

The value attribute of input type="text" and the checked or selected attributes of input type="checkbox", radio and option correspond to the initial value of the form field, not the current value the user or script has set. Consequently changing the checked property does not alter the attribute value, and setting the checked attribute does not alter the real visible value that's going to be submitted with the form.

The checked="checked" attribute corresponds to the defaultChecked DOM property, not the checked property. Similarly, the value="..." attribute corresponds to defaultValue.

(Note there are IE gotchas here due to IE not knowing the difference between a property and an attribute.)

Fillip

I never mentioned the value attribute. My test checkbox doesn't even have one. So I'm not sure how your first paragraph applies, but the defaultChecked property was key. Thanks! – Ferrule

It's background: checked/defaultChecked is the special case of value/defaultValue for checkboxes (similarly selected/defaultSelected for options). – Fillip

Kev, your question is about what is being reported by Firebug. The entirety of bobince's original answer is relevant. Also, additional information is never bad. – Daemon

Please read my question and show me where I mention the value attribute. As for Firebug see my comment on the question. – Ferrule

Answer 2

You may be expecting Firebug to display value information similarly to how style is updated in the HTML inspection pane. However, input, select, option, and textarea do not behave the same way and values will not be updated in this pane and will always display the original values (those at page render time). If the UI is updating, then you know you're doing it right.

Daemon

This just isn't true. Try it yourself with an HTML element a with no value attribute--run the lines a, a.value=7, and a again. – Ferrule

Sorry, what I said still stands, but I should clarify that a was a JavaScript variable pointing to an HTML input elemnt. It probably came across as if I meant an anchor tag. – Ferrule

It did come across that way, but I've delete that comment as it is no longer necessary. However, I don't understand the scenario that you are trying to describe in your first comment, particularly with "and a again" – Daemon

I sure get confused with this comment deletion...makes it difficult to understand the ones that remain. Anyway, the second time you execute a on the firebug command line is to see the difference in a that a.value=7 made... – Ferrule

Answer 3

checked = '', is correct I believe. I suspect the browser is trying to be friendly when you do checked = false and doing the equivalent action, checked = ''.

Blowzed

Tried it. Doesn't seem to change the outcome. Also according to developer.mozilla.org/en/XUL/checkbox , the checked property is a boolean type. – Ferrule

Maybe I'm confused. Is something not working how you expect? – Blowzed

Sorry, I had tried to express that in the question. I expect setting the .checked property to have an effect on the HTML attribute (especially since it has an effect on the UI.) But the HTML attribute does not change, no matter what it's initially set to. This seems pretty inconsistent. – Ferrule

@Kev: make sure you're looking at the right documentation. You linked to the XUL docs there. – Crosslegged

@nickf: Oops, you're absolutely right! In the right docs ( developer.mozilla.org/en/DOM/Input ) it's the same, though. – Ferrule