shake.js - Enable shake gesture detection to trigger a callback function. Code based on a gist by iLee @ https://gist.github.com/leecrossley/4078996

shake.js

/*
 *  shake.js - Enable shake gesture detection to trigger a callback function.
 *  Code based on a gist by iLee @ https://gist.github.com/leecrossley/4078996
 *
 *  Sample usage:
 *  var Shaker = require("./shake");
 *  var shaker = new Shaker(
 *          function onShakeSuccess() {
 *              console.debug("Shake motion detected!"); 
 *          },  
 *          function onShakeError() {
 *              console.debug("Shake error");
 *          }); 
 *
 *  if (shaker.isShakable()) {
 *      shaker.startWatch();
 *  } 
 */
var Shake = module.exports = function (successCB, errorCB, options) {
    this.optons = options || { frequency: 100 };
    this.shakeCallBack = successCB;
    this.errorCallBack = errorCB;
    this.lastVal = { x: null, y: null, z: null };
};

var withThis = function withThis(context, fn) {
    return function() {
        return fn.apply(context, arguments);
    };
};

// Check if accelerometer is supported
Shake.prototype.isShakable = function() {
    return navigator.accelerometer;
};

// Start watching the accelerometer for a shake gesture
Shake.prototype.startWatch = function () {
    if (!this.isShakable()) {
        return;
    }
    this.watchId = navigator.accelerometer.watchAcceleration(withThis(this, 
        this.assessCurrentAcceleration), this.errorCallBack, { frequency: 300 });
};

// Stop watching the accelerometer for a shake gesture
Shake.prototype.stopWatch = function () {
    if (!this.isShakable()) {
        return;
    }
    if (this.watchId) {
        navigator.accelerometer.clearWatch(this.watchId);
        this.watchId = undefined;
    }
};

// Assess the current currVal parameters to determine a shake
Shake.prototype.assessCurrentAcceleration = function (currVal) {
    var delta = {x:0, y:0, z:0};
    if (this.lastVal.x !== null) {
        delta.x = Number(Math.abs(this.lastVal.x - currVal.x));
        delta.y = Number(Math.abs(this.lastVal.y - currVal.y));
        delta.z = Number(Math.abs(this.lastVal.z - currVal.z));
    }
    var deltaTotal = delta.x + delta.y + delta.z;
    if (deltaTotal > 10) {
        // Shake detected
        if (typeof (this.shakeCallBack) === "function") {
            this.shakeCallBack();
        }
        this.stopWatch();
        setTimeout(withThis(this, this.startWatch), 1000, withThis(this, this.shakeCallBack));
        this.lastVal = { x: null, y: null, z: null };
    } else {
        this.lastVal = {x: currVal.x, y: currVal.y, z: currVal.z};
    }
};