data-*

All such custom data are available via the HTMLElement interface of the element the attribute is set on. The HTMLElement.dataset property gives access to them. The * may be replaced by any name following the production rule of XML names which includes the following recommendations:

• The name should not start with xml (case-insensitive), as it's reserved for future XML specifications.
• The name should not contain any colon characters (:), as XML assigns meaning to such names.
• The name should not contain any capital letters, as XML is all lowercase.

These are recommendations. If these naming recommendations are not followed, no errors will occur. The attributes will still be matched using CSS attribute selectors, with the attribute being case insensitive and any attribute value being case-sensitive. Attributes not conforming to these three recommendations will also still be recognized by the JavaScript HTMLElement.dataset property and user-agents will include the attribute in the DOMStringMap containing all the custom data attributes for an HTMLElement.

If you plan to use HTMLElement.dataset, the portion of the attribute name following the data- can only include characters allowed in JavaScript property names (and hyphens, which will be removed). The dataset version of the attribute name removes the "data-" prefix and converts the rest of the name from kebab-case to camelCase. For example, element.getAttribute("data-test") is equivalent to element.dataset.test and data-test-abc will be accessible as HTMLElement.dataset.testAbc (or by HTMLElement.dataset["testAbc"]). Avoid non-alphabetic characters following a hyphen, such as data-test-1 or data--test, as they will not be recognized by HTMLElement.dataset.

By adding data-* attributes, even ordinary HTML elements can become rather complex and powerful program-objects. For example, a space-ship "sprite" in a game could just be an <img> element with a class attribute and several data-* attributes:

<img
  class="spaceship cruiserX3"
  src="shipX3.png"
  data-ship-id="324"
  data-weapons="laserI laserII"
  data-shields="72%"
  data-x="414354"
  data-y="85160"
  data-z="31940"
  onclick="spaceships[this.dataset.shipId].blasted()" />

For a more in-depth tutorial about using HTML data attributes, see Using data attributes.

• All global attributes.
• The HTMLElement.dataset property that allows to access and modify these values.
• Using data attributes