Easy JavaScript gesture recognition for iphone and ipad.
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CONTRIBUTORS Added Up/Down support for Swipe Jan 25, 2013
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jester.js Added Up/Down support for Swipe Jan 25, 2013


// Jester //

Simple Gesture Recognition in JavaScript (for iOS)

var element = document.getElementById("target");
jester(element).tap(function() {
    alert("You hit the target!");

For further documentation check the Jester GitHub Wiki: http://wiki.github.com/plainview/Jester/

 -1 - Before Using
0.0 - Intro
0.1 - The Gestures
1.0 - Project Status
1.1 - Project Aims
1.2 - Project Todos
2.0 - How To Use
2.1 - Basic Syntax
2.2 - Handlers
2.3 - Options
2.4 - TouchGroup Object
2.5 - Touch Object
3.0 - Bugs, Questions

 -1 Before Using

Jester is now 2 years old.  It has received a few patches during that time but I've largely ignored it since release.  There are many newer and more actively maintained projects for this sort of thing.  For example,

http://eightmedia.github.com/hammer.js/ - Hammer.js - for all manner of multi-touch goodness.
https://github.com/jairajs89/Touchy.js - Touchy.js - simple light-weight lib for dealing with touch.
http://zeptojs.com/#touch - Zepto.js - for a jQuery-lite library with basic gesture support.

0.0 Intro

A small JavaScript library for easily recognising gestures on DOM elements on the iPhone and iPad.

0.1 The Gestures

Jester has the following gestures available for immediate use:


All gesture handlers get passed in the Jester touches object.  The touches object has all the good data in it, like how far a touch has moved, how long its been held down and so on.  Read more about that below.
Some of the handlers are also passed in a direction as their second parameter.  This is a string that describes the direction the gesture travelled.  For examples of how this works, see the included index.html file's source.

In addition, Jester also has three customisable methods which give you access to both the touches object and the raw event object:


These handlers are called when the touch starts, when the touch moves and when the touch ends, respectively.  Again, see the index.html file accompanying this repo for their usage.

1.0 Project Status

Jester works for Swipes, Flicks, Taps, Double Taps and Pinches.

Examples of code can be seen at the bottom of this README in the "How to Use" section.

1.1 Project Aims

- Super easy gesture recognition on DOM Elements.
- Elegant syntax.
- Library agnostic : must not rely on jQuery, Moo, Dojo etc.

A basic example can be viewed in the index.html page.  Boot it up on an iPhone, iPad or Simulator and swipe, flick, tap and doubletap on the black square.

This is very much a learning project.  Mistakes will be made and enjoyed whole-heartedly.

1.2 Project Todos

- Clear and thorough documentation.
- Project website.
- Provide "during" methods for all the events (except pinch, which is already available)
- Provide the user a way to write their own custom gesture events

2.0 How to Use

Jester makes recognising gestures on DOM elements really easy.  First you need to know how to get a DOM element, though.  To get an element by its ID, use:

// will assign the element with an ID of "wrapper" to the variable el
var el = document.getElementById("wrapper");

If you're using jQuery or another library which wraps elements in a custom object/interface, you need to get to the DOM element directly.

In jQuery:

// will assign the element with an ID of "wrapper" to the variable el
var el = $("#wrapper")[0];

In Dojo:

// will assign the element with an ID of "wrapper" to the variable el
var el = dojo.query("#wrapper")[0];

OK, on with the Jester information....

2.1 Basic Syntax
  .swipe(swipeHandler)  // attach a handler to the element's swipe event
  .doubletap(dtHandler);  // attach a handler to the element's doubletap event

2.2 Handlers

var handler = function(touchGroup, direction) {
  // handler code

Handlers are passed a TouchGroup object which contains information about the gesture including touch position(s), changes in position and speed.  For swipe and flick events, a direction is also passed as a string (i.e. "left" or "right").

// Log the direction in which a gesture occured
var whichDirection = function(touches, direction) {
    console.log("Swiped to the " + direction);

// Log how far one of the touches in a gesture travelled
var howFar = function(touches, direction) {
    var distanceTravelled = touches.touch(0).total.x();

// Attach the new handlers to some events

2.3 Options
You can also pass Jester options which affect the way gestures are recognised:

jester(document.getElementById("wrapper"), { swipeDistance: 400, flickTime: 200 })

Currently supported Options are:

capture        Boolean   Whether or not to receive events on the capture phase.

tapDistance    Integer   Maximum distance a finger is allowed to travel for a tap to be registered.
tapTime        Integer   Maximum time a finger is allowed to have contact with the screen for a tap to be registered.

doubleTapTime  Integer   The maximum time between two taps to register as a double tap.

swipeDistance  Integer   The minimum distance a gesture must travel before a swipe is registered.

flickTime      Integer   The maximum length of time a gesture can last for it to be registered as a flick.
flickDistance  Integer   The minimum distance a gesture must travel for it to be registered as a flick.

2.4 TouchGroup Object

Every touch handler is passed a TouchGroup object as well as any extra data such as direction info.

The TouchGroup object contains all the computed information about a collection of touches such as
change in scale and rotation.  It also provides access to all of the individual touches and their

Methods of the TouchGroup object:

TouchGroup.numTouches()     : Return the number of touches in the group

TouchGroup.touch(n)         : Get Touch object number n

            scale()         : The current scale factor
            midX()          : The mid x point between the touches (if there is only one touch, the mid point is the touch's position)
            midY()          : The mid y point between the touches (if there is only one touch, the mid point is the touch's position)

            scale()         : The change in the scale factor since the previous move

2.5 Touch Object

Working with a TouchGroup invariably leads to working with the individual Touch objects as well.  As described
above, these are accessed by calling the touch method on a TouchGroup and passing in a number representing which
Touch you want to access.

The Touch object contains all the computed information about a single touch, such as change in position,
duration and speed.

Methods of the Touch object:

            x()         : the starting x position (pageX)
            y()         : the starting y position (pageY)
            time()      : the time the touch started
            speedX()    : the initial x speed (always presumed to be 0)
            speedY()    : the initial y speed (always presumed to be 0)

            x()         : the currrent pageX position
            y()         : the current pageY position
            time()      : the current time
            speedX()    : the current x speed
            speedY()    : the current y speed

            x()         : the previous pageX position
            y()         : the previous pageY position
            time()      : the previous recorded time
            speedX()    : the previous x speed
            speedY()    : the previous y speed

            x()         : the change in x position since the last move
            y()         : the change in y position since the last move
            time()      : the change in time since the last move
            speedX()    : the change in x speed since the last move
            speedY()    : the change in y speed since the last move

            x()         : the total x distance travelled
            y()         : the total y distance travelled
            time()      : the total time of this touch

3.0 Bugs, Questions

Got comments, questions or suggestions?  Get in touch via Github - http:/github.com/plainview/Jester