Question

What I want is to store the sum for a database object with id 3. (see input tags below)
I have many different id’s with different values. The value in the sample below I want to store is 2.

Besides that I want to increase/decrease the value of sum[3] using a “+” and a “-” button with JavaScript. So I created a function called incr and decr to do that:

<script type="text/javascript">
function incr(what)
{
    alert(what);
    what.value ++;

    // rest of the function I left out, it works with a 'normal' name of the input tag
    //but I need to use the array
}    
</script>

how many?<input type="text" size="10" name="sum[3]" value="2" />
<input name="plus" type="button" value="+" onclick="incr(document.sum[3])" />
<input name="min" type="button" value="-" onclick="decr(document.sum[3])" />

I can’t get it working, even the alert doesn’t return a value. Anybody?

Answer 1

This is not the most elegant approach as it is using lots of inline code, but it solves your problem. What went wrong with your approach is that document.sum[3] is not the correct selector the the name=”sum[3]” input

<script type="text/javascript">
function incr(what)
{

    what.value ++;
    alert(what.value);
    // rest of the function I left out, it works with a 'normal' name of the input tag
    //but I need to use the array
}    
</script>

how many?<input type="text" size="10" name="sum[3]" value="2" />
<input name="plus" type="button" value="+" onclick="incr(document.getElementsByName('sum[3]')[0])" />
<input name="min" type="button" value="-" onclick="decr(document.getElementsByName('sum[3]')[0])" />

You should consider using jQuery and refactoring the code with event handlers rather than using inline javascript.