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

Minimalistic but perfect custom scrollbar plugin

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

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

function bindKeyboardHandler(element, i) {
  var hovered = false;
  i.event.bind(element, 'mouseenter', function () {
    hovered = true;
  });
  i.event.bind(element, 'mouseleave', function () {
    hovered = false;
  });

  var shouldPrevent = false;
  function shouldPreventDefault(deltaX, deltaY) {
    var scrollTop = element.scrollTop;
    if (deltaX === 0) {
      if (!i.scrollbarYActive) {
        return false;
      }
      if ((scrollTop === 0 && deltaY > 0) || (scrollTop >= i.contentHeight - i.containerHeight && deltaY < 0)) {
        return !i.settings.wheelPropagation;
      }
    }

    var scrollLeft = element.scrollLeft;
    if (deltaY === 0) {
      if (!i.scrollbarXActive) {
        return false;
      }
      if ((scrollLeft === 0 && deltaX < 0) || (scrollLeft >= i.contentWidth - i.containerWidth && deltaX > 0)) {
        return !i.settings.wheelPropagation;
      }
    }
    return true;
  }

  i.event.bind(i.ownerDocument, 'keydown', function (e) {
    if (e.isDefaultPrevented && e.isDefaultPrevented()) {
      return;
    }

    if (!hovered) {
      return;
    }

    var activeElement = document.activeElement ? document.activeElement : i.ownerDocument.activeElement;
    if (activeElement) {
      // go deeper if element is a webcomponent
      while (activeElement.shadowRoot) {
        activeElement = activeElement.shadowRoot.activeElement;
      }
      if (h.isEditable(activeElement)) {
        return;
      }
    }

    var deltaX = 0;
    var deltaY = 0;

    switch (e.which) {
    case 37: // left
      deltaX = -30;
      break;
    case 38: // up
      deltaY = 30;
      break;
    case 39: // right
      deltaX = 30;
      break;
    case 40: // down
      deltaY = -30;
      break;
    case 33: // page up
      deltaY = 90;
      break;
    case 32: // space bar
    case 34: // page down
      deltaY = -90;
      break;
    case 35: // end
      if (e.ctrlKey) {
        deltaY = -i.contentHeight;
      } else {
        deltaY = -i.containerHeight;
      }
      break;
    case 36: // home
      if (e.ctrlKey) {
        deltaY = element.scrollTop;
      } else {
        deltaY = i.containerHeight;
      }
      break;
    default:
      return;
    }

    element.scrollTop = element.scrollTop - deltaY;
    element.scrollLeft = element.scrollLeft + deltaX;
    updateGeometry(element);

    shouldPrevent = shouldPreventDefault(deltaX, deltaY);
    if (shouldPrevent) {
      e.preventDefault();
    }
  });
}

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