JavaScript Access

Reading those out in JavaScript is also very simple. You could use getAttribute() to read them but the standard defines a simpler way: a DOMStringMap you can read out via a dataset property:

var article = document.querySelector('#electriccars'),
data = article.dataset;

// data.columns -> "3"
// data.indexnumber -> "12314"
// data.parent -> "cars"

Each property is a string (even if you omit the quotes in the HTML) and can be read and written. In the above case setting article.dataset.columns = 5 would change that attribute.

via Using data-* attributes – Web developer guide | MDN.