How do I enable/disable checkboxes when another checkbox is selected?

checkbox, javascript

Solution

All in all, not too difficult.

http://jsfiddle.net/A5TGf/19/

HTML:

<form action="./" id="checkForm" method="post">
    <fieldset>
        <label for="foo">foo</label>
        <input type="checkbox" id="foo" value="foo" />
        <label for="bar">bar</label>
        <input type="checkbox" id="bar" value="bar" />
        <label for="baz">baz</label>
        <input type="checkbox" id="baz" value="baz" />
    </fieldset>
</form>

JS:

var form = document.getElementById("checkForm");
form.onclick = delegateFormClick;

addChangeHandlers(form);

function addChangeHandlers(form)
{
   for(var i=0;i<form.elements.length;i++)
   {
       var element = form.elements[i];
       if(element.tagName === "INPUT" && element.type === "checkbox")
       {
           if(!element.onchange)
           {
               element.onchange = checkBoxChanged;   
           }
       }
   }  
}

function delegateFormClick(evt)
{
    var target;
    if(!evt)
    {
        //Microsoft DOM
        target = window.event.srcElement;
    }else if(evt)
    {
        //w3c DOM
        target = evt.target;
    }
    if(target.nodeType === 1 && target.tagName === "INPUT" && target.type === "checkbox")
    {
        if(target.checked)
        {
            disableCheckBoxes(target.id, document.getElementById("checkForm"));
        }else if(!target.checked)
        {
            enableCheckBoxes(document.getElementById("checkForm"));
        }  
    }
}

function checkBoxChanged()
{
    if(this.checked)
    {
       disableCheckBoxes(this.id, document.getElementById("checkForm"));
    }else if(!this.checked)
    {
        enableCheckBoxes(document.getElementById("checkForm"));  
    }
}

function disableCheckBoxes(id, form)
{
    var blacklist = [];
    if(id)
    {
        switch(id)
        {
            case "foo":
            blacklist = ["bar", "baz"];
            break;
            case "bar":
            blacklist = ["foo"];
            break;
            case "baz":
            blacklist = ["foo", "bar"];
            break;
        }   
    }else
    {
        throw new Error("id is needed to hard-wire input blacklist");   
    }
    for(var i=0;i<blacklist.length;i++)
    {
        var element = document.getElementById(blacklist[i]);
        if(element && element.nodeType === 1)
        {
            //check for element
            if(element.tagName === "INPUT" && element.type === "checkbox" && !element.checked)
            {
                element.disabled = "disabled";
            }
        }else if(!element || element.nodeType !== 1)
        {
            throw new Error("input blacklist item does not exist or is not an element");
        }
    }   
}

function enableCheckBoxes(form)
{
    for(var i=0;i<form.elements.length;i++)
    {
        var element = form.elements[i];
        if(element.tagName === "INPUT" && element.type === "checkbox" && !element.checked)
        {
            element.disabled = "";
        }
    }   
}

Some quick notes on what I'm doing:

- I'm using event delegation to minimize the amount of event handlers. The form listens for a click event bubbling up, then calls a function depending on which element was clicked and its `checked` DOM property.

- I'm traversing the HTMLFormElement.elements collection to easily access the checkboxes.

- I'm setting the `disabled` DOM property to "disabled" on the checkbox if it's not the target checkbox.

- I'm setting the `disabled` DOM property to "" (an empty string) on the checkbox if no checkboxes are checked.

- This also works if the user selects the checkbox by tabbing/entering or another method via the `onchange` handler.

- This code should work in IE, though I'm having some serious problems with IE via Wine at work, so I'll have to test later.

- It uses a "blacklist", which is an array that contains ids to checkboxes you don't want enabled when the corresponding checkbox is clicked.

Let me know if you're looking for anything further.

Problem

Original source

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