transition-scroll-to.js

( function( window, undefined ) {

'use strict';

// helper function
function capitalize( str ) {
  return str.charAt(0).toUpperCase() + str.slice(1);
}

// ========================= getStyleProperty by kangax ===============================
// http://perfectionkills.com/feature-testing-css-properties/

var prefixes = 'Moz Webkit O Ms'.split(' ');

function getStyleProperty( propName ) {
  var style = document.documentElement.style,
      prefixed;

  // test standard property first
  if ( typeof style[propName] === 'string' ) {
    return propName;
  }

  // capitalize
  propName = capitalize( propName );

  // test vendor specific properties
  for ( var i=0, len = prefixes.length; i < len; i++ ) {
    prefixed = prefixes[i] + propName;
    if ( typeof style[ prefixed ] === 'string' ) {
      return prefixed;
    }
  }
}

var transformProp = getStyleProperty('transform');
var transitionProp = getStyleProperty('transition');

var cssTransformProp = {
  WebkitTransform: '-webkit-transform',
  MozTransform: '-moz-transform',
  MsTransform: '-ms-transform',
  OTransform: '-o-transform',
  transform: 'transform'
}[ transformProp ];

var transitionEndEvent = {
  WebkitTransition: 'webkitTransitionEnd',
  MozTransition: 'transitionend',
  OTransition: 'otransitionend',
  transition: 'transitionend'
}[ transitionProp ];

// console.log( transformProp, transitionProp );

function transitionScrollTo( options ) {
  var opts = {};

  // get options from defaults
  for ( var prop in transitionScrollTo.defaults ) {
    opts[ prop ] = transitionScrollTo.defaults[ prop ];
  }
  // overwrite with argument options
  for ( prop in options ) {
    opts[ prop ] = options[ prop ];
  }

  var elem = opts.element;
  // enable transition
  elem.style[ transitionProp + 'Property' ] = cssTransformProp;
  elem.style[ transitionProp + 'Duration' ] = opts.duration;
  // no more than scrolling to the bottom
  var targetX = Math.min( opts.x, elem.clientWidth - window.innerWidth );
  var targetY = Math.min( opts.y, elem.clientHeight - window.innerHeight );
  // no less than top left corner
  targetX = Math.max( targetX, 0 );
  targetY = Math.max( targetY, 0 );
  // account for current scroll position
  targetX -= window.scrollX;
  targetY -= window.scrollY;

  elem.style[ transformProp ] = 'translate( ' + -targetX + 'px, ' + -targetY + 'px)';

  var onTransitionEnd = function( event ) {
    // disregard transition end on child elements
    if ( event.target !== elem ) {
      return;
    }
    // clean up transform and transition styles
    elem.style[ transformProp ] = null;
    elem.style[ transitionProp + 'Duration' ] = null;
    elem.style[ transitionProp + 'Property' ] = null;

    // apply scroll to window
    window.scrollTo( opts.x, opts.y );
    // remove listener
    elem.removeEventListener( transitionEndEvent, onTransitionEnd, false );
  };

  elem.addEventListener( transitionEndEvent, onTransitionEnd, false );
}

transitionScrollTo.defaults = {
  element: document.body,
  x: 0,
  y: 0,
  duration: '0.4s'
};

window.transitionScrollTo = transitionScrollTo;

})( window );