Question

I need to check a certain selection of checkboxes using JavaScript. All these checkboxes have the letter a at the beginning of the id and other checkboxes have a different letter.I also don’t know how many of these checkboxes there will be since they are created dynamically

<input type="checkbox" id="a1" />

Now if I click on a button a JavaScript function is called and these checkboxes with letter a at beginning of id’s should be checked, is this possible and how?

Is there something that can be used in conjunction with document.getElementById('a').checked?

Answer 1

You can get the checkboxes and loop through them, like this:

var checks = document.getElementsByTagName('input');
for(var i = 0, cb; cb = checks[i]; i++) {
   if(cb.type.toLowerCase() == 'checkbox' && cb.id && cb.id.charAt(0) == 'a')
     cb.checked = true;
}

You can give it a try here

Edit: a bit cleaner to use .charAt(), good call and thanks Tim!