dist/scrollify.es6.js
function fade(progress) {
  var to = (this.options.to !== undefined) ? this.options.to : 0;
  var from = (this.options.from !== undefined) ? this.options.from : 1;
  var opacity = (to - from) * progress + from;

  this.element.style.opacity = opacity;
}
function fade(progress) {
  var to = (this.options.to !== undefined) ? this.options.to : 0;
  var from = (this.options.from !== undefined) ? this.options.from : 1;
  var opacity = (to - from) * progress + from;

  this.element.style.opacity = opacity;
}
function fade ( progress ) { var to = ( this . options . to !== undefined ) ? this . options . to : 0 ; var from = ( this . options . from !== undefined ) ? this . options . from : 1 ; var opacity = ( to - from ) * progress + from ; this . element . style . opacity = opacity ; }
Update an element's opacity.
@param {Float} progress  Current progress data of the scene, between 0 and 1.
@this {Object}
@return {void}
Update an element s opacity .