Question

I am trying to dynamically have my javascript look for an element ID in the DOM.

I am currently using this

var string = "retail";
document.getElementById('markup_'+string+'_percentage').value=z.toFixed(2)+"%";

Where the variable “string” has a value like “retail”

This I thought would give a concatenated string of “markup_retail_percentage”.

However it actually gives this as an error message:

document.getElementById("markup_"+string+"_percentage") is null

I have tried also using the “.” and ” * ” operators.

One of my html elements

<input type="text" id="markup_retail_percentage" size="5" name="markup_retail_percentage" value="" readonly />

SOLUTION!!!!

//using a new variable name to be passed to function 
function percentage(elementid)
{

    elementid = "markup_" + elementid;
    elementid = elementid + "_percentage";

document.getElementById(elementid).value = "a value";


}

Answer 1

I see two^w three^w four possibilities:

1. string doesn’t contain what you think it does
2. you should have an underscore before percentage.
3. the specified element really doesn’t exist! (thanks @jAndy)
4. it does, but the DOM isn’t ready yet (thanks @Yoshi)