scrollhandler.jsx

  revealHandleMouseScroll: function(e) {
    var now = new Date().getTime();
    var revealLastRun = this.state.revealLastRun;
    var revealLastScrollEvent = now - this.state.revealLastScrollEvent;
    var revealLastScrollEventStrength = this.state.revealLastScrollEventStrength;
    // Scroll direction is from sitepoint.com/html5-javascript-mouse-wheel/
    var scrollDirection = Math.max(-1, Math.min(1, (e.wheelDelta || -e.detail)));
    var scrollDistance = null;
    var scrollStrength = null;
    var hasInertialScroll = false;
    var activateRevealScroll = false;

    e.preventDefault();

    // Account for stupid browsers not having consistency in how they measure scroll
    if (e.deltaY !== undefined) {
      scrollDistance = e.deltaY;
    } else if (e.wheelDelta !== undefined) {
      scrollDistance = e.wheelDelta * -1;
    }

    if (scrollDistance !== null) {
      scrollStrength = scrollDistance * -1 * scrollDirection;
    }

    // Try to determine if we're dealing with inertial scroll
    if (scrollStrength !== null) {
      hasInertialScroll = (scrollStrength !== revealLastScrollEventStrength || scrollStrength < 20) && revealLastScrollEvent < 50;
    }

    if (hasInertialScroll === true && now - revealLastRun > this.state.revealSettings.throttle) {
      // Only run if the user put in more input, not if we're riding the tail of an old input
      activateRevealScroll = scrollStrength > revealLastScrollEventStrength;
    } else if (now - revealLastRun > this.state.revealSettings.throttle) {
      activateRevealScroll = true;
    }

    // Set the time of the last scroll event
    this.setState({
      revealLastScrollEvent: new Date().getTime(),
      revealLastScrollEventStrength: scrollStrength
    });

    if (activateRevealScroll) {
      // revealScroll() will set revealScrollLastRun
      if (scrollDirection < 0) {
        this.revealScroll(1);
      } else if (scrollDirection > 0) {
        this.revealScroll(-1);
      }
    }

  },