78

I've an element in the DOM:

<a href="#" data-a="1">Link</a>

I want to get this element via its HTML5 custom data attribute data-a. So I write JS codes:

var a = document.querySelector('a[data-a=1]');

But this code doesn't work and I get an error in browser's console. (I tested Chrome and Firefox.)

JS code var a = document.querySelector('a[data-a=a]'); doesn't cause error. So I think the problem is that HTML5's JS API document.querySelector doesn't support to look for the number value in HTML5 custom data attribute.

Is this a problem of browser implementation bug or a problem of HTML5's spec relevant to document.querySelector?

Then I tested codes below on http://validator.w3.org/:

<!DOCTYPE html>
<meta charset="utf-8">
<title>An HTML Document</title>
<a href="#" data-a="1">Link</a>

They're validated. Since these HTML5 codes are validated. We should can use HTML5's JS API document.querySelector to look for this anchor element via its custom data attribute. But tha fact is that I get error.

Does HTML5's spec to HTML5 JS API document.querySelector say that this method can not look for an HTML5 data custom attribute with a number value? (An HTML5 spec source is wanted.)

BoltClock
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weilou
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    when using [CSS attribute selectors](http://www.blooberry.com/indexdot/css/syntax/selectors/attribute.htm), the value should be wrapped in quotes, e.g. `a[data-a="1"]`. – Eliran Malka Feb 11 '13 at 09:53
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    `querySelectorAll()` is not an "HTML5 JS API". It has absolutely nothing to do with HTML5 whatsoever. – BoltClock Jul 20 '13 at 12:24

6 Answers6

157

From the selectors specification:

Attribute values must be CSS identifiers or strings.

Identifiers cannot start with a number. Strings must be quoted.

1 is therefore neither a valid identifier nor a string.

Use "1" (which is a string) instead.

var a = document.querySelector('a[data-a="1"]');
Quentin
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    and if your number is stored in a variable eg var dataId = 5; then it should be written out this way document.querySelector("a[data-a='"+dataId+"']"); this answer helped but I had trouble with the quotes for a bit hope this helps someone – James Daly Jul 28 '14 at 22:45
  • Note, this can also be written as `document.querySelector("a[data-a=\"1\"]");`. – Marc.2377 Jun 26 '19 at 23:15
7

You could use

var a = document.querySelector('a[data-a="1"]');

instead of

var a = document.querySelector('a[data-a=1]');
Nikita
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0

Because you need parentheses around the value your looking for. So here : document.querySelector('a[data-a="1"]')

If you don't know in advance the value but is looking for it via variable you can use template literals :

Say we have divs with data-price

<div data-price="99">My okay price</div>
<div data-price="100">My too expensive price</div>

We want to find an element but with the number that someone chose (so we don't know it):

// User chose 99    
let chosenNumber = 99
document.querySelector(`[data-price="${chosenNumber}"`]
Earth_Believer
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-2

Took me a while to find this out but if you a number stored in a variable, say x and you want to select it, use 

document.querySelector('a[data-a= + CSS.escape(x) + ']').

This is due to some attribute naming specifications that I'm not yet very familiar with. Hope this will help someone.

Donat
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-3

Yes strings must be quoted and in some cases like in applescript, quotes must be escaped

do JavaScript "document.querySelector('span[" & attrName & "=\"" & attrValue & "\"]').click();"
vhanahrni
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-3

An example with variable (ES6):

const item = document.querySelector([data-itemid="${id}"]);

Oksana
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