bmfe-vue2-base/src/js/baseLibs/sidebarMenu/perfectScrollbar/plugin/update-scroll.js

BM 后台系统基础框架

'use strict';

var instances = require('./instances');

var upEvent = document.createEvent('Event');
var downEvent = document.createEvent('Event');
var leftEvent = document.createEvent('Event');
var rightEvent = document.createEvent('Event');
var yEvent = document.createEvent('Event');
var xEvent = document.createEvent('Event');
var xStartEvent = document.createEvent('Event');
var xEndEvent = document.createEvent('Event');
var yStartEvent = document.createEvent('Event');
var yEndEvent = document.createEvent('Event');
var lastTop;
var lastLeft;

upEvent.initEvent('ps-scroll-up', true, true);
downEvent.initEvent('ps-scroll-down', true, true);
leftEvent.initEvent('ps-scroll-left', true, true);
rightEvent.initEvent('ps-scroll-right', true, true);
yEvent.initEvent('ps-scroll-y', true, true);
xEvent.initEvent('ps-scroll-x', true, true);
xStartEvent.initEvent('ps-x-reach-start', true, true);
xEndEvent.initEvent('ps-x-reach-end', true, true);
yStartEvent.initEvent('ps-y-reach-start', true, true);
yEndEvent.initEvent('ps-y-reach-end', true, true);

module.exports = function (element, axis, value) {
  if (typeof element === 'undefined') {
    throw 'You must provide an element to the update-scroll function';
  }

  if (typeof axis === 'undefined') {
    throw 'You must provide an axis to the update-scroll function';
  }

  if (typeof value === 'undefined') {
    throw 'You must provide a value to the update-scroll function';
  }

  if (axis === 'top' && value <= 0) {
    element.scrollTop = value = 0; // don't allow negative scroll
    element.dispatchEvent(yStartEvent);
  }

  if (axis === 'left' && value <= 0) {
    element.scrollLeft = value = 0; // don't allow negative scroll
    element.dispatchEvent(xStartEvent);
  }

  var i = instances.get(element);

  if (axis === 'top' && value >= i.contentHeight - i.containerHeight) {
    // don't allow scroll past container
    value = i.contentHeight - i.containerHeight;
    if (value - element.scrollTop <= 1) {
      // mitigates rounding errors on non-subpixel scroll values
      value = element.scrollTop;
    } else {
      element.scrollTop = value;
    }
    element.dispatchEvent(yEndEvent);
  }

  if (axis === 'left' && value >= i.contentWidth - i.containerWidth) {
    // don't allow scroll past container
    value = i.contentWidth - i.containerWidth;
    if (value - element.scrollLeft <= 1) {
      // mitigates rounding errors on non-subpixel scroll values
      value = element.scrollLeft;
    } else {
      element.scrollLeft = value;
    }
    element.dispatchEvent(xEndEvent);
  }

  if (!lastTop) {
    lastTop = element.scrollTop;
  }

  if (!lastLeft) {
    lastLeft = element.scrollLeft;
  }

  if (axis === 'top' && value < lastTop) {
    element.dispatchEvent(upEvent);
  }

  if (axis === 'top' && value > lastTop) {
    element.dispatchEvent(downEvent);
  }

  if (axis === 'left' && value < lastLeft) {
    element.dispatchEvent(leftEvent);
  }

  if (axis === 'left' && value > lastLeft) {
    element.dispatchEvent(rightEvent);
  }

  if (axis === 'top') {
    element.scrollTop = lastTop = value;
    element.dispatchEvent(yEvent);
  }

  if (axis === 'left') {
    element.scrollLeft = lastLeft = value;
    element.dispatchEvent(xEvent);
  }

};