PageLifecycle.js

Overview
Installation
Usage
API
Browser Support

Overview

PageLifecycle.js is a tiny JavaScript library (<1K gzipped) that allows developers to easily observe Page Lifecycle API state changes and implement Page Lifecycle best practices consistently across all browsers.

▶️ View demo: page-lifecycle.glitch.me 👀

Installation

You can install this library from npm by running:

npm install --save-dev page-lifecycle

Usage

Releases of this library include three minified, production-ready versions:

1. ES5: dist/lifecycle.es5.js (UMD) ⭐

Use this version for maximum compatibility with legacy browsers (that can't run ES2015+ code).

As a UMD bundle, it can be required in CommonJS or AMD environments, or it can be loaded with a script tag as the browser global lifecycle.

<script defer src="/path/to/lifecycle.es5.js"></script>
<script defer>
lifecycle.addEventListener('statechange', function(event) {
  console.log(event.oldState, event.newState);
});
</script>

2. ES2015: dist/lifecycle.mjs (ESM) 🔥

Use this version if you only support ES module-capable browsers or if you're using <script type="module"> and the nomodule fallback to conditionally target modern browsers.

<script type="module">
import lifecycle from '/path/to/page-lifecycle.mjs';

lifecycle.addEventListener('statechange', function(event) {
  console.log(event.oldState, event.newState);
});
</script>

3. ES2015 (native): dist/lifecycle.native.mjs (ESM w/o EventTarget and Event shims) ⚠️

Use this version if you're only targeting browsers that support extending EventTarget and Event constructors.

Note: this version is the smallest but will only work in some browsers. The implementation instructions are the same as the ES2015 version above.

API

The PageLifecycle.js library exports a lifecycle object, which is a singleton instance of the Lifecycle class. The Lifecycle class has the following properties, methods, and events:

Properties

Name	Type	Description
`state`	`string`	Returns the current Page Lifecycle state.
`pageWasDiscarded`	`boolean`	Returns the value of `document.wasDiscarded` (or `false` if not present).

Methods

Name	Description
`addEventListener`	Parameters: type: `string` listener: `function(Event)` Adds a callback function to be invoked whenever the passed event type is detected. (Note: at the moment only the "statechange" event type is supported.)
`removeEventListener`	Parameters: type: `string` listener: `function(Event)` Removes a function from the current list of listeners for the passed event type. (Note: at the moment only the "statechange" event type is supported.)
`addUnsavedChanges`	Parameters: id: `Object\|Symbol` Adds an item to an internal pending-changes stack. Calling this method adds a generic `beforeunload` listener to the window (if one isn't already added). The argument passed should be unique to this state, as it can only be removed by passing the same argument to `removeUnsavedChanges()`.
`removeUnsavedChanges`	Parameters: id: `Object\|Symbol` Removes an item matching the passed argument from an internal pending-changes stack. If the stack is empty, the generic `beforeunload` listener is removed from the window.

Events

Name Description

Name	Description
`statechange`	Properties: newState: `string` The current lifecycle state the page just transitioned to. oldState: `string` The previous lifecycle state the page just transitioned from. originalEvent: `Event` the DOM event that triggered the state change. The `statechange` event is fired whenever the page's lifecycle state changes.

statechange

Properties:

newState: string The current lifecycle state the page just transitioned to.
oldState: string The previous lifecycle state the page just transitioned from.
originalEvent: Event the DOM event that triggered the state change.

The statechange event is fired whenever the page's lifecycle state changes.