Shake.js

/*
*
* Find more about this plugin by visiting
* http://alxgbsn.co.uk/
*
* Copyright (c) 2010-2012 Alex Gibson
* Released under MIT license
*
*/

(function (window, document) {

function Shake() {

    //feature detect
    this.hasDeviceMotion = 'ondevicemotion' in window;

    //default velocity threshold for shake to register
    this.threshold = 15;

    //use date to prevent multiple shakes firing    
    this.lastTime = new Date();

    //accelerometer values
    this.lastX = null;
    this.lastY = null;
    this.lastZ = null;

    //create custom event
    this.event = document.createEvent('Event');
    this.event.initEvent('shake', true, true);
}

//reset timer values
Shake.prototype.reset = function () {

    this.lastTime = new Date();
    this.lastX = null;
    this.lastY = null;
    this.lastZ = null;
};

//start listening for devicemotion
Shake.prototype.start = function () {

    this.reset();
    if (this.hasDeviceMotion) { window.addEventListener('devicemotion', this, false); }
};

//stop listening for devicemotion
Shake.prototype.stop = function () {

    if (this.hasDeviceMotion) { window.removeEventListener('devicemotion', this, false); }
    this.reset();
};

//calculates if shake did occur
Shake.prototype.devicemotion = function (e) {

    var current = e.accelerationIncludingGravity,
        currentTime,
        timeDifference,
        deltaX = 0,
        deltaY = 0,
        deltaZ = 0;

    if ((this.lastX === null) && (this.lastY === null) && (this.lastZ === null)) {

        this.lastX = current.x;
        this.lastY = current.y;
        this.lastZ = current.z;
        return;
    }

    deltaX = Math.abs(this.lastX - current.x);
    deltaY = Math.abs(this.lastY - current.y);
    deltaZ = Math.abs(this.lastZ - current.z);

    if (((deltaX > this.threshold) && (deltaY > this.threshold)) || ((deltaX > this.threshold) && (deltaZ > this.threshold)) || ((deltaY > this.threshold) && (deltaZ > this.threshold))) {

        //calculate time in milliseconds since last shake registered
        currentTime = new Date();
        timeDifference = currentTime.getTime() - this.lastTime.getTime();

        if (timeDifference > 1000) {
            window.dispatchEvent(this.event);
            this.lastTime = new Date();
        }
    }
};

//event handler
Shake.prototype.handleEvent = function (e) {

    if (typeof (this[e.type]) === 'function') {
        return this[e.type](e);
    }
};

//create a new instance of shake.js.
var myShakeEvent = new Shake();
myShakeEvent.start();

}(window, document));