Why does JS code "var a = document.querySelector('a[data-a=1]');" cause error?
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.)
Answer
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"]');