HTMLElement.dataset

The HTMLElement.dataset property allows access, both in reading and writing mode, to all the custom data attributes (data-*) set on the element, either in HTML or in the DOM. It is a map of DOMString, one entry for each custom data attribute. Note that the dataset property itself can be read, but not directly written. Instead, all writes must be to its "properties", which in turn represent the data attributes. Note also that an HTML data-attribute and its corresponding DOM dataset.property do not share the same name, but they are always similar:

• The name of a custom data attribute in HTML begins with data-. It must contain only letters, numbers and the following characters: dash (-), dot (.), colon (:), underscore (_) -- but NOT any ASCII capital letters (A to Z).
• The name of a custom data attribute in Javascript is the name of the same HTML attribute but in camelCase and with no dashes, dots, etc.

In addition to the information below, you'll find a how-to guide for using HTML data attributes in our article Using data attributes.

Name conversion

dash-style to camelCase: A custom data attribute name is transformed to a key for the DOMStringMap entry with the following rules

• the prefix data- is removed (including the dash);
• for any dash (U+002D) followed by an ASCII lowercase letter a to z, the dash is removed and the letter is transformed into its uppercase counterpart;
• other characters (including other dashes) are left unchanged.

camelCase to dash-style: The opposite transformation, that maps a key to an attribute name, uses the following rules:

• Restriction: A dash must not be immediately followed by an ASCII lowercase letter a to z (before the transformation);
• a prefix data- is added;
• any ASCII uppercase letter A to Z is transformed into a dash followed by its lowercase counterpart;
• other characters are left unchanged.

The restriction in the rules above ensures that the two transformations are the inverse one of the other.

For example, the attribute named data-abc-def corresponds to the key abcDef.

Accessing values

• Attributes can be set and read by using the camelCase name (the key) like an object property of the dataset, as in element.dataset.keyname
• Attributes can also be set and read using the object-properties bracket-syntax, as in element.dataset[keyname]

Syntax

• string = element.dataset.camelCasedName;
• element.dataset.camelCasedName = string;


• string = element.dataset[camelCasedName];
• element.dataset[camelCasedName] = string;


• Custom data attributes can also be set directly on HTML elements, but attribute names must use the data- syntax above.

Examples

<div id="user" data-id="1234567890" data-user="johndoe" data-date-of-birth>John Doe</div>

let el = document.querySelector('#user');

// el.id == 'user'
// el.dataset.id === '1234567890'
// el.dataset.user === 'johndoe'
// el.dataset.dateOfBirth === ''

el.dataset.dateOfBirth = '1960-10-03'; // set the DOB.

// 'someDataAttr' in el.dataset === false
el.dataset.someDataAttr = 'mydata';
// 'someDataAttr' in el.dataset === true

Specifications

Browser compatibility

See also

• The HTML data-* class of global attributes.
• Using data attributes