Simple Drifting, used in several tests written in CasperJS for the https://github.com/azoff/Overscroll jQuery Plugin. Can be used in Node.JS and in the browser.

drifting.js

/**
 * A wrapper function to make easy drifts.
 * Works as a nodejs or browser module.
 * @author vardump
 * @param  {object} options {
      startCoordinates: { //optional
        x: Number,
        y: Number
      },
      degree: Number,  // degree of direction to drift.
      distance: Number,   // distance in pixel
      duration: Number,   // duration of drift in seconds
      start: Function,    // Callback for start, arguments x,y
      way: Function,      // Callback for the way, arguments x,y
      finished: Function, // Callback when finished, arguments x,y
      waitFinished: Number// time to wait between last way() and finished call
    }
 */
function drift (options, window) {
  var MOVE_INTERVAL = 2; //ms
  var speed = options.distance / options.duration;
  options.degree = ((Math.PI * 2) / 360) * options.degree;
  var stepX = Math.sin(options.degree);
  var stepY = -Math.cos(options.degree);

  var moveCoeficent = (MOVE_INTERVAL / 1000) * speed;
  var interval;
  var x, y;
  var counter = 0;
  options.duration = options.duration * 1000;

  var limit = Math.floor(options.duration / MOVE_INTERVAL);
  var that = this;

  // if no start point was given, start at 0
  if (options.hasOwnProperty('startCoordinates')) {
    if (options.startCoordinates.hasOwnProperty('x') &&
      options.startCoordinates.hasOwnProperty('y') &&
      typeof options.startCoordinates.x === 'number' &&
      typeof options.startCoordinates.y === 'number') {
        x = options.startCoordinates.x;
        y = options.startCoordinates.y;
    } else {
      x = 0;
      y = 0;
    }
  } else {
    x = 0;
    y = 0;
  }

  stepX = stepX * moveCoeficent;
  stepY = stepY * moveCoeficent;

  //start
  if (options.hasOwnProperty('start') &&
    typeof options.start === 'function') {
    //call start callback
    options.start(x, y);
  }

  var returnVal = true;

  interval = setInterval(function () {
    //console.log(stepX, stepY);
    if (counter <= limit) {
      x += stepX;
      y += stepY;
      //call the way callback    
      options.way(x, y);
      counter += 1;
    } else {  
      if (options.hasOwnProperty('waitFinished')) {
        setTimeout(function () {
          options.finished(x, y);
        }, options.waitFinished);
      } else {
        options.finished(x, y);
      }
      if (window) {
        window.clearInterval(interval);
      } else {
        clearInterval(interval);
      }
      returnVal = true;
    }
  }, MOVE_INTERVAL);
  return returnVal;
}

//the frontend doesnt know any module ..
if (typeof module !== 'undefined') {
    module.exports = drift;
}