Javascript check / uncheck checkboxes based on id

Question

I have many server input checkboxes. I have given the first checkbox the id all. By default it will be checked. When the user checks other checkboxes, then checkbox with id all will be unchecked. And if all is checked other checkboxes will be unchecked. For this to happen i made the code but nothing is happening.

Here is what i have tried.

<form>
<input type="checkbox" id="all" value="all" name="all" onChange="check()" checked/>ALL <br/>
<input type="checkbox" id="servers" value="xampp" name="server[]" onChange="check()" />XAMPP <br/>
<input type="checkbox" id="servers" value="wamp" name="server[]" onChange="check()" />WAMP <br/>
<input type="checkbox" id="servers" value="mamp" name="server[]" onChange="check()" />MAMP <br/>
<input type="checkbox" id="servers" value="amp" name="server[]" onChange="check()" />AMP <br/>
</form>


function check(){
    var all = document.getElementById("all"),
        group = document.getElementById("servers");
    if(all.checked == true){
        group.checked == false;
    }elseif(group.checked == true){
        all.checked == false;
    }
}

I wanted my code to work like THIS.

I dont want to use jQuery for some reasons. So i need my code to be in pure JS.

Any help will be appreciated.

Answer 1

You can't use the same ID on multiple elements.

Try this, notice how I placed the checkboxes in a div

Here it is working: http://jsfiddle.net/Sa2d3/

HTML:

<form>
    <div id="checkboxes">
        <input type="checkbox" id="all" value="all" name="all" onChange="check()" />ALL <br/>
        <input type="checkbox" value="xampp" name="server[]" onChange="check()" />XAMPP <br/>
        <input type="checkbox" value="wamp" name="server[]" onChange="check()" />WAMP <br/>
        <input type="checkbox" value="mamp" name="server[]" onChange="check()" />MAMP <br/>
        <input type="checkbox" value="amp" name="server[]" onChange="check()" />AMP <br/>
    </div>
</form>

JavaScript:

document.getElementById('checkboxes').addEventListener('change', function(e) {
    var el = e.target;
    var inputs = document.getElementById('checkboxes').getElementsByTagName('input');

    // If 'all' was clicked
    if (el.id === 'all') {

        // loop through all the inputs, skipping the first one
        for (var i = 1, input; input = inputs[i++]; ) {

            // Set each input's value to 'all'.
            input.checked = el.checked;
        }
    }

    // We need to check if all checkboxes have been checked
    else {
        var numChecked = 0;

        for (var i = 1, input; input = inputs[i++]; ) {
            if (input.checked) {
                numChecked++;
            }
        }

        // If all checkboxes have been checked, then check 'all' as well
        inputs[0].checked = numChecked === inputs.length - 1;
    }
}, false);

EDIT:

Based on your request in the comment here is the updated javascript: http://jsfiddle.net/T5Pm7/

document.getElementById('checkboxes').addEventListener('change', function(e) {
    var el = e.target;
    var inputs = document.getElementById('checkboxes').getElementsByTagName('input');

    // If 'all' was clicked
    if (el.id === 'all') {

        // If 'all' is checked
        if (el.checked) {

            // Loop through the other inputs and removed the check
            for (var i = 1, input; input = inputs[i++]; ) {
                input.checked = false;
            }
        }
    }

    // If another has been clicked, remove the check from 'all'
    else {
        inputs[0].checked = false;
    }
}, false);