Do html5 data attributes need a value? [duplicate]

Answer 1

No. But...

As is common with all attributes, in the application/xhtml+xml serialisation, XML rules apply and the attribute must have an explicit name and (quoted) value.

So this question is really about the text/html serialisation, and therefore the relevant part of the HTML5 spec is Section 8 The HTML syntax

In particular, under attributes, it says:

Attributes can be specified in four different ways:

where the first of these is:

Empty attribute syntax

   Just the attribute name. The value is implicitly the empty string.

It's necessary to understand though that the value is of string type, not of boolean type.

For example, with , the "checked" attribute is reflected by a property that is either true or false. So

if (document.getElementById("cb").checked)

will evaluate to true for the above markup.

In contrast, with , the "data-checked" attribute is reflected via the dataset object as a string. The value of this property is the empty string, which in JavaScript is falsey. So,

if (document.getElementById("cb").dataset.checked)

will evaluate to false for the above markup.

To do the equivalent test, compare the value for "not undefined". I.e.

if (document.getElementById("cb").dataset.checked !== undefined)

will evaluate to true for the above markup.

See http://jsfiddle.net/GAxvW/