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scroll to top

当前为 2020-06-20 提交的版本，查看 最新版本。

  1. // ==UserScript==
  2. // @name         Back to top
  3. // @namespace    cyyyu
  4. // @version      0.3
  5. // @description  scroll to top
  6. // @author       Chuang Yu
  7. // @match        https://*/*
  8. // @grant        none
  9. // @run-at       document-end
  10. // ==/UserScript==
  11.  
  12. (function() {
  13.     'use strict';
  14.  
  15.     /* written in es5 */
  16.  
  17.     var rootNode = document.querySelector("html")
  18.     var prevLocations = new Map() // node: number
  19.     var timers = new Map() // node: number
  20.     var backToPrevLocationDelay = 10000 // 10s
  21.  
  22.     rootNode.addEventListener("dblclick", function (evt) {
  23.         var path = evt.path
  24.  
  25.         for (var i = 0; i < path.length; i++) {
  26.             var node = path[i]
  27.             if (!isScrollable(node)) continue;
  28.             if (!evt.altKey) return
  29.  
  30.             if (!isAtTop(node)) {
  31.                 clearTimeout(timers.get(node))
  32.                 scrollTo(node, 0)
  33.             } else if (prevLocations.has(node)) {
  34.                 scrollTo(node, prevLocations.get(node))
  35.             }
  36.         }
  37.     })
  38.  
  39.     function isAtTop(node) {
  40.         return node.scrollTop === 0
  41.     }
  42.  
  43.     function scrollTo(node, top) {
  44.         var prevScrollBehavior = node.style.scrollBehavior
  45.         var prevLocation = node.scrollTop
  46.  
  47.         node.style.scrollBehavior = "smooth"
  48.         node.scrollTop = top
  49.         node.style.scrollBehavior = prevScrollBehavior
  50.  
  51.         if (top === 0) {
  52.             prevLocations.set(node, prevLocation)
  53.             var timer = setTimeout(
  54.                 function () { prevLocations.delete(node) },
  55.                 backToPrevLocationDelay
  56.             )
  57.             timers.set(node, timer)
  58.         }
  59.     }
  60.  
  61.     function isScrollable(node) {
  62.         return (
  63.             (node.scrollHeight - node.clientHeight > 100) &&
  64.             (node.clientHeight > 50)
  65.         )
  66.     }
  67.  
  68. })();