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?

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.)

Answer 2

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 = ''.

Answer 3

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.