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Editorial Team
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Asked: 2026-05-25T06:10:23+00:00

I want to create a selection list. When an item on the list is

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I want to create a selection list. When an item on the list is clicked same should be showing in a text box, when another item is clicked even that should be added to text box. I am trying to work out the code below but somehow its not doing its job. Any help will be highly appreciated.

<html>
<head>

<script type="text/javascript">

function register_click(num){
document.getElementById('boxclicked').value += num; 

}

</script>

</head>

<body>
<td><ul>

<li id="2" onclick="register_click(1)">List item 1</li>
<li id="3" onclick="register_click(2)">List item 2</li>
<li id="4"onclick="register_click(3)">List Item 3</li>

</ul></td>

<input type='text' size="150%" width="100%" maxlength="" id="boxclicked">

</body>

</html>
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1 Answer

  1. Editorial Team

    I’m assuming that you want to do arithmetic, but you’re function is actually doing string concatenation. For arithmetic you need to make sure that any ‘number’ is actually a number and not a string:

    function register_click(num){
    var box = document.getElementById('boxclicked');
    box.value = box.value || 0
    box.value = parseInt(box.value, 10) + num;
}

    box.value will be undefined on first click, so we make sure that it has a value, even if that value is 0. parseInt converts a string to a number, we pass 10 to make sure that it does it in base 10.

    JavaScript is funny sometimes, for instance:

    "1" + 2 + 3 === "123" // true
2 + 3 + "1" === "51" // true

    It always tries to coerce types, sometimes this is good, but it can lead to confusion like the above, when it works counter-intuitively. This is what you were running into with your original code. The value of the element was a string, which caused num to become a string and be concatenated.

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