Array element as a parameter for getElementById().checked

Question

I'm having trouble referencing a checkbox element from an array of element ids. Why can I reference it using a literal and string var as the parameter of getElementById, but not by using an element of an array?

<html>
<body>

<ul id="zip_wrapper">
<li><label><input type="checkbox" id="72002" value="72002" name="zip_codes[]" checked="checked">72002</label></li>
<li><label><input type="checkbox" id="72034" value="72034" name="zip_codes[]" checked="checked">72034</label></li>
</ul>
<script>

var zips = "";
var tester = "72034";
zips = document.getElementById("zip_wrapper").innerText.split(" ");

//zips =  Array.prototype.slice.call(zips); //a la http://stackoverflow.com/questions/4287681/extremely-annoying-javascript-array-object-error

document.write("zips array, tokenized by split(\" \"): " + zips + "<br />");

document.write("document.getElementById(\"72034\").checked: " + document.getElementById("72034").checked + "<br />");
document.write("document.getElementById(tester).checked: " + document.getElementById(tester).checked + "<br />");
document.write("document.getElementById(zips[1]).checked: " + document.getElementById(zips[1]).checked + "<br />");

</script>
</body>
</html>

You can see the page in action here: https://dl.dropbox.com/u/1634015/website/checked.html

The reason for why you can't use zips[1]? --> console.log(zips) or console.log(zips.length) ;) — Andreas
– Andreas, Commented Jun 11, 2012 at 21:57
Firefox returns undefined for the "innerText" of the <ul> element ... — Pointy
– Pointy, Commented Jun 11, 2012 at 22:00

CWSpear · Accepted Answer · 2012-06-11 22:05:38Z

1

When I go to your test page, when I do

zips = document.getElementById("zip_wrapper").innerText.split(" ");

in the console, I'm getting zips as an element of length one, so zips[1] would be undefined. It seems (at least in Chrome) that innerText is returning each one on its own line. I split by \n and I got:

["72002", "72034", ""]

I think the bottom line is the issue isn't that you're using an element from an array, but that you array isn't made up like you are expecting it to be.

And as Pointy pointed out, it seems that Firefox just returns undefined and I found Chrome to return them on each their own line (i.e. separated with "\n" with an empty string at the end).

You might need a different approach to what you're trying to accomplish, but the answer to the original question, is that there's nothing wrong with using an array element as a parameter of getElementById.

edited Jun 11, 2012 at 22:05

answered Jun 11, 2012 at 21:53

CWSpear

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3 Comments

user898763452 Over a year ago

That is a purposefully literal string, as in showing the javascript that I am trying to output.

Pointy Over a year ago

No, that's not the problem; that part is just the label on the line he's printing out.

CWSpear Over a year ago

yeah, I just realized I misread that part. I think the problem has to do with creating the zips array. zips[1] doesn't exist when he's outputting it as I'm seeing it.

Stephan · Accepted Answer · 2012-09-27 10:32:57Z

0

The argument must be a string literal e.g.

wanted=document.getElementById("myhtmlobject").value

so if you have an array of similar objects rather than just one,

myhtmlobject[1]
myhtmlobject[2]
myhtmlobject[3]
myhtmlobject[4]
etc

then reference them like this

myobj="myhtmlobject[" + j + "]"
wanted= document.getElementById(myobj).value

edited Sep 27, 2012 at 10:32

Stephan

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answered Aug 29, 2012 at 21:44

Peter

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