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DOM events

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Events are fired to notify code of “interesting changes” that may affect code execution. These can arise from user interactions such as using a mouse or resizing a window, changes in the state of the underlying environment (e.g., low battery or media events from the operating system), and other causes.

Each event is represented by an object that is based on the Event interface, and may have additional custom fields and/or functions to provide information about what happened. The documentation for every event has a table (near the top) that includes a link to the associated event interface, and other relevant information. A full list of the different event types is given in Event > Interfaces based on Event.

This topic provides an index to the main sorts of events you might be interested in (animation, clipboard, workers etc.) along with the main classes that implement those sorts of events.

Event index

Event type Description Documentation
Animation

Events related to the Web Animation API.

Used to respond to changes in animation status (e.g., when an animation starts or ends).

Animation events fired on Document, Window, HTMLElement.
Asynchronous data fetching

Events related to the fetching data.

 Events fired on AbortSignal, XMLHttpRequest, FileReader.
Clipboard

Events related to the Clipboard API.

Used to notify when content is cut, copied, or pasted.

 Events fired on Document, Element, Window.
Composition

Events related to composition; entering text "indirectly" (rather than using normal keyboard presses).

For example, text entered via a speech to text engine, or using special key combinations that modify keyboard presses to represent new characters in another language.

Events fired on Element.
CSS transition

Events related to CSS Transitions.

Provides notification events when CSS transitions start, stop, are cancelled, etc.

Events fired on Document, HTMLElement, Window.
Database

Events related to database operations: opening, closing, transactions, errors, etc.

Events fired on IDBDatabase, IDBOpenDBRequest, IDBRequest, IDBTransaction.
DOM mutation

Events related to modifications to the Document Object Model (DOM) hierarchy and nodes.

Warning: Mutation Events are deprecated. Mutation Observers should be used instead.

Drag'n'drop, Wheel

Events related to using the HTML Drag and Drop API and wheel events.

Drag and Wheel events are derived from mouse events. While they are fired when using mouse wheel or drag/drop, they may also be used with other appropriate hardware.

Drag events fired on Document

Wheel events fired on Element

Focus

Events related to elements gaining and losing focus.

 Events fired on Element, Window.
Form

Events related to forms being constructed, reset and submitted.

 Events fired on HTMLFormElement.
Fullscreen

Events related to the Fullscreen API.

Used to notify when the transitioning between full screen and windowed modes, and also of errors occurring during this transition.

Events fired on Document, Element.
Gamepad

Events related to the Gamepad API.

Events fired on Window.
Gestures

Touch events are recommended for implementing gestures.

Events fired on Document, Element.

In addition there are a number of non-standard gesture events:
History

Events related to the History API.

Events fired on Window.
HTML element content display management

Events related to changing the state of a display or textual element.

Events fired on HTMLDetailsElement, HTMLDialogElement, HTMLSlotElement.
Inputs

Events related to HTML input elements e.g. [``](/firefox/mdn/html/reference/elements/input/), [`

In addition to the events fired by built-in interfaces, you can create and dispatch DOM events yourself. Such events are commonly called synthetic events, as opposed to the events fired by the browser.

Creating custom events

Events can be created with the Event constructor as follows:

const event = new Event("build");

// Listen for the event.
elem.addEventListener("build", (e) => {
  /* … */
});

// Dispatch the event.
elem.dispatchEvent(event);

This code example uses the EventTarget.dispatchEvent() method.

Adding custom data – CustomEvent()

To add more data to the event object, the CustomEvent interface exists and the detail property can be used to pass custom data. For example, the event could be created as follows:

const event = new CustomEvent("build", { detail: elem.dataset.time });

This will then allow you to access the additional data in the event listener:

function eventHandler(e) {
  console.log(`The time is: ${e.detail}`);
}

Adding custom data – subclassing Event

The Event interface can also be subclassed. This is particularly useful for reuse, or for more complex custom data, or even adding methods to the event.

class BuildEvent extends Event {
  #buildTime;

  constructor(buildTime) {
    super("build");
    this.#buildTime = buildTime;
  }

  get buildTime() {
    return this.#buildTime;
  }
}

This code example defines a BuildEvent class with a read-only property and a fixed event type.

The event could then be created as follows:

const event = new BuildEvent(elem.dataset.time);

The additional data can then be accessed in the event listeners using the custom properties:

function eventHandler(e) {
  console.log(`The time is: ${e.buildTime}`);
}

Event bubbling

It is often desirable to trigger an event from a child element and have an ancestor catch it; optionally, you can include data with the event:

<form>
  <textarea></textarea>
</form>

const form = document.querySelector("form");
const textarea = document.querySelector("textarea");

// Create a new event, allow bubbling, and provide any data you want to pass to the "detail" property
const eventAwesome = new CustomEvent("awesome", {
  bubbles: true,
  detail: { text: () => textarea.value },
});

// The form element listens for the custom "awesome" event and then consoles the output of the passed text() method
form.addEventListener("awesome", (e) => console.log(e.detail.text()));

// As the user types, the textarea inside the form dispatches/triggers the event to fire, using itself as the starting point
textarea.addEventListener("input", (e) => e.target.dispatchEvent(eventAwesome));

Creating and dispatching events dynamically

Elements can listen for events that haven’t been created yet:

<form>
  <textarea></textarea>
</form>

const form = document.querySelector("form");
const textarea = document.querySelector("textarea");

form.addEventListener("awesome", (e) => console.log(e.detail.text()));

textarea.addEventListener("input", function () {
  // Create and dispatch/trigger an event on the fly
  // Note: Optionally, we've also leveraged the "function expression" (instead of the "arrow function expression") so "this" will represent the element
  this.dispatchEvent(
    new CustomEvent("awesome", {
      bubbles: true,
      detail: { text: () => textarea.value },
    }),
  );
});

Triggering built-in events

This example demonstrates simulating a click (that is programmatically generating a click event) on a checkbox using DOM methods. View the example in action.

function simulateClick() {
  const event = new MouseEvent("click", {
    view: window,
    bubbles: true,
    cancelable: true,
  });
  const cb = document.getElementById("checkbox");
  const cancelled = !cb.dispatchEvent(event);

  if (cancelled) {
    // A handler called preventDefault.
    alert("cancelled");
  } else {
    // None of the handlers called preventDefault.
    alert("not cancelled");
  }
}

Registering event handlers

There are two recommended approaches for registering handlers. Event handler code can be made to run when an event is triggered either by assigning it to the target element’s corresponding onevent property or by registering the handler as a listener for the element using the addEventListener() method. In either case, the handler will receive an object that conforms to the Event interface (or a derived interface). The main difference is that multiple event handlers can be added (or removed) using the event listener methods.

[!WARNING] A third approach for setting event handlers using HTML onevent attributes is not recommended! They inflate the markup and make it less readable and harder to debug. For more information, see Inline event handlers.

Using onevent properties

By convention, JavaScript objects that fire events have corresponding “onevent” properties (named by prefixing “on” to the name of the event). These properties are called to run associated handler code when the event is fired, and may also be called directly by your own code.

To set event handler code, you can just assign it to the appropriate onevent property. Only one event handler can be assigned for every event in an element. If needed, the handler can be replaced by assigning another function to the same property.

The following example shows how to set a greet() function for the click event using the onclick property.

const btn = document.querySelector("button");

function greet(event) {
  console.log("greet:", event);
}

btn.onclick = greet;

Note that an object representing the event is passed as the first argument to the event handler. This event object either implements or is derived from the Event interface.

EventTarget.addEventListener

The most flexible way to set an event handler on an element is to use the addEventListener method. This approach allows multiple listeners to be assigned to an element and enables listeners to be removed, if needed, using removeEventListener.

[!NOTE] The ability to add and remove event handlers allows you to, for example, have the same button performing different actions in different circumstances. In addition, in more complex programs, cleaning up old/unused event handlers can improve efficiency.

The following example shows how a greet() function can be set as a listener/event handler for the click event (you could use an anonymous function expression instead of a named function if desired). Note again that the event is passed as the first argument to the event handler.

const btn = document.querySelector("button");

function greet(event) {
  console.log("greet:", event);
}

btn.addEventListener("click", greet);

The method can also take additional arguments/options to control aspects of how the events are captured and removed. More information can be found on the addEventListener reference page.

Using AbortSignal

A notable event listener feature is the ability to use an abort signal to clean up multiple event handlers at the same time.

This is done by passing the same AbortSignal to the addEventListener() call for all the event handlers that you want to be able to remove together. You can then call abort() on the controller owning the AbortSignal, and it will remove all event handlers that were added with that signal. For example, to add an event handler that we can remove with an AbortSignal:

const controller = new AbortController();

btn.addEventListener(
  "click",
  (event) => {
    console.log("greet:", event);
  },
  { signal: controller.signal },
); // pass an AbortSignal to this handler

This event handler can then be removed like this:

controller.abort(); // removes any/all event handlers associated with this controller

Interaction of multiple event handlers

The onevent IDL property (for example, element.onclick = ...) and the HTML onevent content attribute (for example, <button onclick="...">) both target the same single handler slot. HTML loads before JavaScript could access the same element, so usually JavaScript replaces what’s specified in HTML. Handlers added with addEventListener() are independent. Using onevent does not remove or replace listeners added with addEventListener(), and vice versa.

When an event is dispatched, listeners are called in phases. There are two phases: capture and bubble. In the capture phase, the event starts from the highest ancestor element and moves down the DOM tree until it reaches the target. In the bubble phase, the event moves in the opposite direction. Event listeners by default listen in the bubble phase, and they can listen in the capturing phase by specifying capture: true with addEventListener(). Within a phase, listeners run in the order they were registered. The onevent handler is registered the first time it becomes non-null; later reassignments change only its callback, not its position in the order.

Calling stopPropagation() prevents calling listeners on other elements later in the propagation chain. stopImmediatePropagation() also prevents calling remaining listeners on the same element.

Specifications

SpecificationsStandards references are available on the canonical MDN page.

See also