getElementById not returning element

Question

I am trying to get an elements id from another elements value and I just keeps returning null. Clicking on the first check box should show what the issue is that I am having.

<input id="test" type="checkbox" name="checkAddress" onclick="checkAddress(this)" value="66" /> <input id="rrrr66" type="checkbox" name="checkAddress" onclick="checkAddress(this)" value="33" /> <script> function checkAddress(checkbox) { if (checkbox.checked) { var testing = '"rrrr'+document.getElementById("test").value+'"'; alert(typeof testing); **<-- shows the correct type** alert(testing); **<-- shows the correct value** alert(document.getElementById(testing)); **<-- does not work** alert(document.getElementById("rrrr66")); **<--works** } }

Demo Of issue

Felix Kling · Accepted Answer · 2015-01-28 15:50:23Z

Remove the quotation marks from the string:

var testing = 'rrrr'+document.getElementById("test").value;

Quotation marks are for the parser to indicate a string literal. The quotation marks are not actually part of the value. What you are currently doing is equivalent with

document.getElementById('"rrrr66"')

Compare these two outputs:

console.log("foo bar"); // foo bar console.log('"foo' + ' bar"'); // "foo bar"

rafaeldefazio · Accepted Answer · 2015-01-28 16:03:33Z

0

1

Get the value of test and add rrrr before:

var testing = "rrrr"+document.getElementById("test").value;

2 Do the trick

document.getElementById(testing)

This should work.

edited Jan 28, 2015 at 16:03

answered Jan 28, 2015 at 15:54

rafaeldefazio

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3 Comments

Felix Kling Over a year ago

There a two elements, one has ID rrrr66.

rafaeldefazio Over a year ago

Yes, but you're trying to document.getElementById(testing), when testing var is equal to '"rrrr'+document.getElementById("test").value+'"';, this is like document.getElementById('"rrrr'+document.getElementById("test").value+'"').

Felix Kling Over a year ago

I'm not doing anything. But yes, that is the problem (I guess, not sure what exactly you are referring to), not that there is an element with ID test. Btw, your answer doesn't really include any information. What solution are you proposing?

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