Origami Frontend Components & Services

Readme: ftdomdelegate

FT's dom delegate library is a component for binding to events on all target elements matching the given selector, irrespective of whether anything exists in the DOM at registration time or not. This allows developers to implement the event delegation pattern.

FT DOM Delegate is developed by FT Labs, part of the Financial Times.


The library has been deployed as part of the FT Web App and is tried and tested on the following browsers:

For older browsers (IE8) you'll need the following polyfills

The easiest way is to include the following script tag and let Polyfill.io work its magic

<script src="https://cdn.polyfill.io/v2/polyfill.js?features=Event,Array.prototype.map,Function.prototype.bind,document.querySelector,Element.prototype.matches"></script>


Get the browserify-able source from a package manager:

npm install ftdomdelegate


bower install ftdomdelegate


The library is written in CommonJS and so can be require in.

// If requiring the module via CommonJS, either:-
Delegate = require('ftdomdelegate').Delegate;
myDel = new Delegate(document.body);

// Or:-
delegate = require('ftdomdelegate');
myDel = delegate(document.body);

The script must be loaded prior to instantiating a Delegate object.

To instantiate Delegate on the body and listen to some events:

function handleButtonClicks(event) {
  // Do some things

function handleTouchMove(event) {
  // Do some other things

document.addEventListener('DOMContentLoaded', function() {
  var delegate = new Delegate(document.body);
  delegate.on('click', 'button', handleButtonClicks);

  // Listen to all touch move
  // events that reach the body
  delegate.on('touchmove', handleTouchMove);


A cool trick to handle images that fail to load:

function handleImageFail() {
  this.style.display = 'none';

document.addEventListener('DOMContentLoaded', function() {
  var delegate = new Delegate(document.body);
  delegate.on('error', 'img', handleImageFail);

Note: as of 0.1.2 you do not need to provide a DOM element at the point of instantiation, it can be set later via the root method.

Also note: as of 0.2.0 you cannot specify more than one eventType in a single call to off or on.

Google Closure Compiler

Delegate supports compilation with ADVANCED_OPTIMIZATIONS ('advanced mode'), which should reduce its size by about 70% (60% gzipped). Note that exposure of the Delegate variable isn't forced therefore you must compile it along with all of your code.


Tests are run using buster and sit in test/. To run the tests statically:

$ cd ftdomdelegate/
$ ./node_modules/.bin/buster-static -c test/buster.js
Starting server on http://localhost:8282/

…then point your browser to http://localhost:8282/.

$ ./node_modules/.bin/buster-server
buster-server running on http://localhost:1111

Point your browser to http://localhost:1111 and capture it, then in another terminal tab:

$ ./node_modules/.bin/buster-test -c test/buster.js

Code coverage is generated automatically with istanbul. The report outputs to lcov-report/index.html.


.on(eventType[, selector], handler[, useCapture])

eventType (string)

The event to listen for e.g. mousedown, mouseup, mouseout, error, click, etc.

selector (string)

Any kind of valid CSS selector supported by matchesSelector. Some selectors, like #id or tag will use optimized functions internally that check for straight matches between the ID or tag name of elements.

null is also accepted and will match the root element set by root(). Passing a handler function into .on's second argument is equivalent to .on(eventType, null, handler).

handler (function)

Function that will handle the specified event on elements matching the given selector. The function will receive two arguments: the native event object and the target element, in that order.

useCapture (boolean)

Whether or not to listen during the capturing (pass in true) or bubbling phase (pass in false). If no value passed in, it will fallback to a 'sensible default', which is true for error, blur and focus events and false for all other types.

.off([eventType][, selector][, handler][, useCapture])

Calling off with no arguments will remove all registered listeners, effectively resetting the instance.

eventType (string)

Remove handlers for events matching this type considering the other parameters.

selector (string)

Only remove listeners registered with the given selector, among the other arguments.

If null passed listeners registered to the root element will be removed. Passing in a function into off's second parameter is equivalent to .off(eventType, null, handler[, useCapture]) (the third parameter will be ignored).

handler (function)

Only remove listeners registered with the given handler function, among the other arguments. If not provided, remove all handlers.

useCapture (boolean)

Only remove listeners with useCapture set to the value passed in. If not provided, remove listeners added with useCapture set to true and false.


element (Node)

Set the delegate's root node. If no element passed in the root node will be deleted and the event listeners will be removed.


Short hand for off() and root(), ie both with no parameters. Used to reset the delegate object.

Credits and collaboration

The developers of ftdomdelegate are Matthew Andrews and Matthew Caruana Galizia. Test engineering by Sam Giles. The API is influenced by jQuery Live. All open source code released by FT Labs is licenced under the MIT licence. We welcome comments, feedback and suggestions. Please feel free to raise an issue or pull request.

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Install ftdomdelegate

If using the Build Service, add ftdomdelegate@^3.0.2 to your script tag.

If running a Manual Build, run npm install "ftdomdelegate@^3.0.2".

Help & Support

ftdomdelegate is maintained directly by the Origami team. If you have any questions about ftdomdelegate or Origami in general, we are happy to help. 😊

Slack: #ft-origami
Email: origami.support@ft.com

Feedback / Issues

To report a bug or request features please create an issue on Github. For support or general feedback please get in touch 😊

Slack: #ft-origami
Email: origami.support@ft.com