HTMLOrForeignElement.dataset

The dataset read-only property of the HTMLOrForeignElement interface provides read/write access to all the custom data attributes (data-*) set on the element. This access is available both in HTML and within the DOM. It is a map of DOMStrings (DOMStringMap) with 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 the individual properties within the dataset, 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:

• In HTML, the name of a custom data attribute 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).
• In JavaScript, the name of a custom data attribute 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 conversion

A custom data attribute name is transformed to a key for the DOMStringMap entry with the following rules

1. The prefix data- is removed (including the dash);
2. 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;
3. Other characters (including other dashes) are left unchanged.

camelCase to dash-style conversion

The opposite transformation, which maps a key to an attribute name, uses the following rules:

1. Restriction: Before the transformation, a dash must not be immediately followed by an ASCII lowercase letter a to z;
2. The prefix data- is added;
3. Any ASCII uppercase letter A to Z is transformed into a dash, followed by its lowercase counterpart;
4. 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 bracket syntax, as in element.dataset[keyname]
• The in operator can be used to check whether a given attribute exists.

Setting values

• When an attribute is set, its value is always converted into a string.

  • For example: null is converted into the string "null".

• To remove an attribute, you can use the delete operator.

Syntax

const dataAttrMap = element.dataset

Value

A DOMStringMap.

Examples

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

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

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

// set the data attribute
el.dataset.dateOfBirth = '1960-10-03';
// Result: el.dataset.dateOfBirth === 1960-10-03

delete el.dataset.dateOfBirth;
// Result: el.dataset.dateOfBirth === undefined

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

Specifications

Browser compatibility

See also

• The HTML data-* class of global attributes.
• Using data attributes
• Element.getAttribute() and Element.setAttribute()