The HTMLElement.attachInternals() method returns an ElementInternals object. This method allows a custom element to participate in HTML forms. The ElementInternals interface provides utilities for working with these elements in the same way you would work with any standard HTML form element, and also exposes the Accessibility Object Model to the element.

None.

An ElementInternals object.

NotSupportedError DOMException

Thrown if the element is not a custom element.

NotSupportedError DOMException

Thrown if the "internals" feature was disabled as part of the element definition.

NotSupportedError DOMException

Thrown if this method is called twice on the same element.

The following example demonstrates how to create a custom form-associated element with HTMLElement.attachInternals. The ElementInternals.form property is then printed to the console to demonstrate that we have an ElementInternals object.

class CustomCheckbox extends HTMLElement {
  static formAssociated = true;

  constructor() {
    super();
    this.internals_ = this.attachInternals();
  }
  // …
}

window.customElements.define("custom-checkbox", CustomCheckbox);

let element = document.getElementById("custom-checkbox");
console.log(element.internals_.form);

• More capable form controls
• Creating custom form controls with ElementInternals