PACE

An automatic web page progress bar.

Documentation

Include pace.js and the theme css of your choice on your page (as early as possible), and you're done!

Pace will automatically monitor your ajax requests, event loop lag, document ready state, and elements on your page to decide the progress. On ajax navigation it will begin again!

If you use AMD or Browserify, require pace.js and call pace.start() as early in the loading process as possible.

Example

<head>
  <script src="https://cdn.jsdelivr.net/npm/pace-js@latest/pace.min.js"></script>
  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/pace-js@latest/pace-theme-default.min.css">
</head>

Configuration

Pace is fully automatic, no configuration is necessary to get started.

If you would like to make some tweaks, here's how:

You can set window.paceOptions before bringing in the file:

paceOptions = {
  // Disable the 'elements' source
  elements: false,

  // Only show the progress on regular and ajax-y page navigation,
  // not every request
  restartOnRequestAfter: false
}

You can also put options on the script tag:

<script data-pace-options='{ "ajax": false }' src="https://cdn.jsdelivr.net/npm/pace-js@latest/pace.min.js"></script>

If you're using AMD or Browserify, you can pass your options to start:

define(['pace'], function(pace){
  pace.start({
    document: false
  });
});

Themes

Pace includes a bunch of themes to get you started. Just include the appropriate css file. Send us a PR with any interesting themes you create.

If you have minor styling changes and don't want to extend theme css, you can add custom class names to the progress bar using the "className" option:

paceOptions = {
  className: 'my-custom-class'
}

Collectors

Collectors are the bits of code which gather progress information. Pace includes four default collectors:

Ajax

Monitors all ajax requests on the page
Elements

Checks for the existence of specific elements on the page
Document

Checks the document readyState
Event Lag

Checks for event loop lag signaling that javascript is being executed

They can each be configured or disabled through configuration options of the same name.

paceOptions = {
  ajax: false, // disabled
  document: false, // disabled
  eventLag: false, // disabled
  elements: {
    selectors: ['.my-page']
  }
};

Add your own classes to paceOptions.extraSources to add more sources. Each source should either have a .progress property, or a .elements property which is a list of objects with .progress properties. Pace will automatically handle all scaling to make the progress changes look smooth to the user.

Elements

Elements being rendered to the screen is one way for us to decide that the page has been rendered. If you would like to use that source of information (not required at all), specify one or more selectors. You can comma separate the selectors to properly handle error states, where the progress bar should disappear, but the element we are looking for may never appear:

paceOptions = {
  elements: {
    selectors: ['.timeline, .timeline-error', '.user-profile, .profile-error']
  }
}

Pace will consider the elements test successful when each selector matches something. For this example, when either .timeline or .timeline-error exist, and either .user-profile or .profile-error exist.

Restart Rules

Most users want the progress bar to automatically restart when a pushState event occurs (generally means ajax navigation is occuring). You can disable this:

paceOptions = {
  restartOnPushState: false
}

You can also have pace restart on every ajax request which lasts longer than x ms. You'll want to disable this if you make ajax requests the user doesn't need to know about, like precaching:

paceOptions = {
  restartOnRequestAfter: false
}

You can always trigger a restart manually by calling Pace.restart()

See the source for a full list of options.

API

Pace exposes the following methods:

Pace.start: Show the progress bar and start updating. Called automatically if you don't use AMD or CommonJS.
Pace.restart: Show the progress bar if it's hidden and start reporting the progress from scratch. Called automatically whenever pushState or replaceState is called by default.
Pace.stop: Hide the progress bar and stop updating it.
Pace.track: Explicitly track one or more requests, see Tracking below
Pace.ignore: Explicitly ignore one or more requests, see Tracking below

Events

Pace fires the following events:

start: When pace is initially started, or as a part of a restart
stop: When pace is manually stopped, or as a part of a restart
restart: When pace is restarted (manually, or by a new AJAX request)
done: When pace is finished
hide: When the pace is hidden (can be later than done, based on ghostTime and minTime)

You can bind onto events using the on, off and once methods:

Pace.on(event, handler, [context]): Call handler (optionally with context) when event is triggered
Pace.off(event, [handler]): Unbind the provided event and handler combination.
Pace.once(event, handler, [context]): Bind handler to the next (and only the next) incidence of event

Tracking

By default, Pace will show any ajax requests which begin as a part of a normal or ajax-y page load, or which last longer than 500ms.

You can disable all ajax tracking by setting ajax to false:

Pace.options = {
  ajax: false
}

You can disable ajax tracking except on page navigation by setting restartOnRequestAfter to false:

Pace.options = {
  restartOnRequestAfter: false
}

You can manually disable tracking for a specific request or requests by triggering them within a Pace.ignore callback:

Pace.ignore(function() {
  $.ajax(...)
});

You can force the progress bar to be shown for a specific request by triggering them within a Pace.track callback:

Pace.track(function() {
  $.ajax(...)
});

You can also ignore URLs based on a pattern:

Pace.options = {
  ajax: {
    ignoreURLs: ['some-substring', /some-regexp/]
  }
}

Dependencies

None!

Support

Pace is designed to support IE8+ (standards mode), FF 3.5+, Chrome, Safari 4+, Opera 10.5+, and all modern mobile browsers. If you run into a compatibility issue, or can make a case for supporting something else, please create an issue.

Size

pace.js is 4kb minified and gzipped. The themes vary between 0.5 and 4kb.

Issues

We have obviously not tested this on every website. If you run into an issue, or find a way the automatic detection could be better, please create an Issue. If you can include a test case, that's even better.

Credits

HubSpot

CodeByZach

Javascript by Zack Bloom CSS by Adam Schwartz

Themes inspired by Mary Lou

Project inspired by nprogress

CodeByZach / pace