perfect-scrollbar/src/js/plugin/handler/drag-scrollbar.js

Minimalistic but perfect custom scrollbar plugin

/* Copyright (c) 2015 Hyunje Alex Jun and other contributors
 * Licensed under the MIT License
 */
'use strict';

var d = require('../../lib/dom')
  , h = require('../../lib/helper')
  , instances = require('../instances')
  , updateGeometry = require('../update-geometry');

function bindMouseScrollXHandler(element, i) {
  var currentLeft = null;
  var currentPageX = null;

  function updateScrollLeft(deltaX) {
    var newLeft = currentLeft + deltaX;
    var maxLeft = i.containerWidth - i.scrollbarXWidth;

    if (newLeft < 0) {
      i.scrollbarXLeft = 0;
    } else if (newLeft > maxLeft) {
      i.scrollbarXLeft = maxLeft;
    } else {
      i.scrollbarXLeft = newLeft;
    }

    var scrollLeft = h.toInt(i.scrollbarXLeft * (i.contentWidth - i.containerWidth) / (i.containerWidth - i.scrollbarXWidth));
    element.scrollLeft = scrollLeft;
  }

  var mouseMoveHandler = function (e) {
    updateScrollLeft(e.pageX - currentPageX);
    updateGeometry(element);
    e.stopPropagation();
    e.preventDefault();
  };

  var mouseUpHandler = function () {
    h.stopScrolling(element, 'x');
    i.event.unbind(i.ownerDocument, 'mousemove', mouseMoveHandler);
  };

  i.event.bind(i.scrollbarX, 'mousedown', function (e) {
    currentPageX = e.pageX;
    currentLeft = h.toInt(d.css(i.scrollbarX, 'left'));
    h.startScrolling(element, 'x');

    i.event.bind(i.ownerDocument, 'mousemove', mouseMoveHandler);
    i.event.once(i.ownerDocument, 'mouseup', mouseUpHandler);

    e.stopPropagation();
    e.preventDefault();
  });
}

function bindMouseScrollYHandler(element, i) {
  var currentTop = null;
  var currentPageY = null;

  function updateScrollTop(deltaY) {
    var newTop = currentTop + deltaY;
    var maxTop = i.containerHeight - i.scrollbarYHeight;

    if (newTop < 0) {
      i.scrollbarYTop = 0;
    } else if (newTop > maxTop) {
      i.scrollbarYTop = maxTop;
    } else {
      i.scrollbarYTop = newTop;
    }

    var scrollTop = h.toInt(i.scrollbarYTop * (i.contentHeight - i.containerHeight) / (i.containerHeight - i.scrollbarYHeight));
    element.scrollTop = scrollTop;
  }

  var mouseMoveHandler = function (e) {
    updateScrollTop(e.pageY - currentPageY);
    updateGeometry(element);
    e.stopPropagation();
    e.preventDefault();
  };

  var mouseUpHandler = function () {
    h.stopScrolling(element, 'y');
    i.event.unbind(i.ownerDocument, 'mousemove', mouseMoveHandler);
  };

  i.event.bind(i.scrollbarY, 'mousedown', function (e) {
    currentPageY = e.pageY;
    currentTop = h.toInt(d.css(i.scrollbarY, 'top'));
    h.startScrolling(element, 'y');

    i.event.bind(i.ownerDocument, 'mousemove', mouseMoveHandler);
    i.event.once(i.ownerDocument, 'mouseup', mouseUpHandler);

    e.stopPropagation();
    e.preventDefault();
  });
}

module.exports = function (element) {
  var i = instances.get(element);
  bindMouseScrollXHandler(element, i);
  bindMouseScrollYHandler(element, i);
};