Javascript class to perform parallax scrolling animations on arbitrary css properties

ScalarParallaxAnimation.js

function ScalarParallaxAnimation( selector, cssProp, scaleMin, scaleMax, valueMin, valueMax, isInteger ) {
  isInteger = isInteger || false;
  this.$target = $(selector);
  this.cssProp = cssProp;
  this.scaleMin = scaleMin;
  this.scaleMax = scaleMax;
  this.valueMin = valueMin;
  this.valueMax = valueMax;
  this.isInteger = isInteger;
  this.setCssValue( valueMin );
  this.attachListener();
}

ScalarParallaxAnimation.prototype = {
  setCssValue: function ( value ) {
    this.$target.css( this.cssProp, value );
  },
  // Nice, easy to use wrapper around setScalarCssValue
  setScrollValue: function ( scrollValue ) {
    this._setScalarCssValue(
      scrollValue,
      this.cssProp,
      this.scaleMin,
      this.scaleMax,
      this.valueMin,
      this.valueMax,
      this.isInteger
    );
  },
  _setScalarCssValue: function ( position, cssProperty, scrollMin, scrollMax, valueMin, valueMax, isInteger ) {
    var value = this.getScaledValue( position, scrollMin, scrollMax, valueMax, valueMin, isInteger );
    this.setCssValue( value );
  },

  getScaledValue: function ( current, scaleMin, scaleMax, valueMax, valueMin, isInteger ) {
    function linearScale ( value, scaleMin, scaleMax, valMin, valMax ){
      /**
       *         (b-a)(x - min)
       *  f(x) = --------------  + a
       *            max - min
       */
      var scaled = ( ( ( valMax-valMin )*( value - scaleMin ) ) / ( scaleMax - scaleMin ) + valMin );
      if ( scaled !== scaled ) { scaled = 0; } // Division by 0
      return scaled;

    }

    function clamp( actual, min, max ) {
      var biggest  = max > min ? max : min;
      var smallest = max > min ? min : max;
      actual = Math.min( actual, biggest );
      actual = Math.max( actual, smallest );
      return actual;
    }

    function scaleValue ( value, scaleMin, scaleMax, valMin, valMax ) {
      return clamp( linearScale( value, scaleMin, scaleMax, valMin, valMax ), valMin, valMax );
    }

    var value = scaleValue( current, scaleMin, scaleMax, valueMin, valueMax );

    if ( isInteger ) {
      value = Math.round( value );
    }
    return value;
  },
  attachListener: function () {
    var $window = $(window);
    $window.scroll(function(){
      var scrollY = $window.scrollTop();
      this.setScrollValue( scrollY );
    }.bind(this));
  },
  detatchListener: function() {
    // @TODO: have a function to detach listeners when we are done with the object
  }
};

ueage.js

if (!$) { throw new Error("I need jQuery to work"); }
// usage exmaple:
//    <div id="divOne">Watch me grow from 60 to 120px high when you scroll between 200 pixels away from the top of the screen</div>
var divOneAnimation = new ScalarParallaxAnimation( '#divOne', 'height', 200, 300, 60, 120, true );
// example 2:
//    <div id="divTwo">It works with floats, as well as from high to low values. Watch me fade out</div>
var divTwoAnimation = new ScalarParallaxAnimation( '#divTwo', 'opacity', 200, 300, 1, 0, false );
// for more control, you can also manually set the property
divTwoAnimation.setScrollValue(250);
// which, in this case is the same as
divTwoAnimation.setCssValue(0.5)