Change/Get check state of CheckBox

Question

I just want to get/change value of CheckBox with JavaScript. Not that I cannot use jQuery for this. I've tried something like this but it won't work.

JavaScript function

    function checkAddress()     {         if (checkAddress.checked == true)         {             alert("a");         }     } 

HTML

<input type="checkbox" name="checkAddress" onchange="checkAddress()" /> 

Answer 1

Using onclick instead will work. In theory it may not catch changes made via the keyboard but all browsers do seem to fire the event anyway when checking via keyboard.

You also need to pass the checkbox into the function:

function checkAddress(checkbox) {     if (checkbox.checked)     {         alert("a");     } } 

HTML

<input type="checkbox" name="checkAddress" onclick="checkAddress(this)" /> 

Answer 2

You need to retrieve the checkbox before using it.

Give the checkbox an id attribute to retrieve it with document.getElementById(..) and then check its current state.

For example:

function checkAddress() {     var chkBox = document.getElementById('checkAddress');     if (chkBox.checked)     {         // ..     } } 

And your HTML would then look like this:

<input type="checkbox" id="checkAddress" name="checkAddress" onclick="checkAddress()"/> 

(Also changed the onchange to onclick. Doesn't work quite well in IE :).