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Editorial Team
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Asked: 2026-05-26T05:40:06+00:00

In the following example: <html> <head> <SCRIPT language=JavaScript> function checkcheckboxElem(checkboxElem) { alert (checkboxElem +

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In the following example:

<html>
<head>
<SCRIPT language="JavaScript">
function checkcheckboxElem(checkboxElem)
{
    alert ("checkboxElem " + checkboxElem.length);  

}
</script>
</head>
<body>
    <form name="checkForm">
        Master: <input type="checkbox" name="master" value="6694" onclick="checkcheckboxElem(document.checkForm.checkboxElem)"><br>

        Child1: <input type="checkbox" name="checkboxElem" value="2">
    </form>                             
</body>

The alert outputs ‘undefined’. For some reason it does this if there is only one checkbox. If i add another checkbox then it outputs the correct length. If i change it as shown below then it outputs 2

<html>
<head>
<SCRIPT language="JavaScript">
function checkcheckboxElem(checkboxElem)
{
    alert ("checkboxElem " + checkboxElem.length);  

}
</script>
</head>
<body>
    <form name="checkForm">
        Master: <input type="checkbox" name="master" value="6694" onclick="checkcheckboxElem(document.checkForm.checkboxElem)"><br>

        Child1: <input type="checkbox" name="checkboxElem" value="2">
Child2: <input type="checkbox" name="checkboxElem" value="1">
    </form>

Why does it return ‘undefined’ if it is only one checkbox?

Thanks

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1 Answer

  1. Editorial Team

    In the first case document.checkForm.checkboxElem refers to a single input element, in the second case it refers to an array of input elements. You could do:

    function checkcheckboxElem(checkboxElem) {
    if(!checkboxElem.length)
        checkboxElem = [checkboxElem];
    alert ("checkboxElem " + checkboxElem.length);  
}
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