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I have a form field (a series of checkboxes) that's being created dynamically from a database, so it's possible that the field will not exist on the form (if there are no matching values in the database). I have some code that needs to execute based on whether the field exists, and pull in the values that are selected if it does exist. I can't seem to get javascript to acknowledge that this field exists, though. Here's what I've tried:

function displayAction(){
    var f = document.adminForm;
    var a = f.action;

    if(f.prefix.value!="-") {
        a = a + '&task=callExclusionDisplay&prefix=' + f.prefix.value;
    }
    else {
        var exclusions = document.getElementById("exclusions");
        if (exclusions != null){
            alert("exclusions set");
            a = a + '&task=callExclusionCreate&prefix=' + f.prefix.value + '&exclusions=' + exclusions.join();
        }
    }
    alert('after if, action is ' + a);
}

The code never passes the if statement checking to see if exclusions is not null, even though when I look at the page there are a number of checkboxes named exclusions (with the id also set to exclusions). Is the issue with !=null because it's a group of checkboxes, rather than a single form element? How can I get this to work? If I skip the test for null, the code throws errors about exclusions not being defined if the database doesn't return any matching values.

I have a form field (a series of checkboxes) that's being created dynamically from a database, so it's possible that the field will not exist on the form (if there are no matching values in the database). I have some code that needs to execute based on whether the field exists, and pull in the values that are selected if it does exist. I can't seem to get javascript to acknowledge that this field exists, though. Here's what I've tried:

function displayAction(){
    var f = document.adminForm;
    var a = f.action;

    if(f.prefix.value!="-") {
        a = a + '&task=callExclusionDisplay&prefix=' + f.prefix.value;
    }
    else {
        var exclusions = document.getElementById("exclusions");
        if (exclusions != null){
            alert("exclusions set");
            a = a + '&task=callExclusionCreate&prefix=' + f.prefix.value + '&exclusions=' + exclusions.join();
        }
    }
    alert('after if, action is ' + a);
}

The code never passes the if statement checking to see if exclusions is not null, even though when I look at the page there are a number of checkboxes named exclusions (with the id also set to exclusions). Is the issue with !=null because it's a group of checkboxes, rather than a single form element? How can I get this to work? If I skip the test for null, the code throws errors about exclusions not being defined if the database doesn't return any matching values.

• javascript

Share Improve this question Follow asked Aug 25, 2010 at 17:26 EmmySEmmyS 12.2k4949 gold badges103103 silver badges161161 bronze badges

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5 Answers 5

Sorted by: Reset to default 3

You're using document.getElementById, but form elements have a name. Try f.elements.namedItem("exclusions") instead of exclusions != null

Multiple elements in the same page cannot share an id attribute (ie. id must be unique or unset). As well, though some (older) browsers erroneously collect elements whose name matches the ID being looked for with getElementById, this is invalid and will not work cross-browser.

If you want to get a group of elements, you can give them all the same name attribute, and use document.getElementsByName to get the group. Note that the result of that will be a NodeList which is kind of like an array in that it can be iterated over.

Do all the checkboxes have the same id == exclusions? If yes, then you must first correct that.

Before you do so, did you try checking the first checkbox and see if the if condition goes through?

if you have more than one element with the id "exclusions" it will screw up the functionality of getElementById. I would remove the duplicate "exclusions" ids from all of your elements and use getElementByName() instead, and give your group of checkboxes the name="exclusions" instead.

Edit: But there is a much simpler way using jQuery, and it gives you some cross browser pability guarrantee. To do the same thing with jQuery do this:

var checkBoxesExist = $('[name=exclusions]').count() > 0;

Or if you have given your elements unique ID's then you can do this:

var checkbox1exists = $('#checkBox1').count() > 0;

Each element must have a unique ID.

Then, you can check just like this:

if (document.getElementById('exclusions1')) {
    //field exists
}

Or if you need to loop through a bunch of them:

for (x=0; x<10; x++) {
    if (document.getElementById('exclusions' + x)) {
        //field X exists
    }
}

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