Next Image/Previous Image

Quick scroll to next/previous image on a page with n/p buttons (now also looks for canvas and iframe elements)
当前为 2018-01-11 提交的版本，查看最新版本。
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// ==UserScript==
// @name Next Image/Previous Image
// @author arty <me@arty.name>
// @namespace http://arty.name/
// @version 2.0.7
// @description  Quick scroll to next/previous image on a page with n/p buttons (now also looks for canvas and iframe elements)
// @include *
// ==/UserScript==
 
// This is a minor adaptation of arty's original, by joeytwiddle
 
// 2012/10 - Now sorting positions so out-of-order images do not break the sequence.
 
(function(){
  // Original keys: forward and back
  // var forwardButton  = 102; // F
  // var backwardButton = 114; // R
  // Current keys: next and previous
  var forwardButton  = 110; // N
  var backwardButton = 112; // P
  // For Vim / Facebook / 9gag lovers:
  // var forwardButton  = 106; // J
  // var backwardButton = 107; // K
  var leeway = 2; // This is needed if you have zoomed out the page.  (We might try to set scrollTop to 100, but it will only move to 99.)
 
  var positions = [];
 
  document.addEventListener('keypress', function(event){
    if (event.ctrlKey || event.shiftKey || event.altKey) return;
    var code = event.keyCode || event.which;
    if (code != backwardButton && code != forwardButton) return;
    if (event.target.tagName && event.target.tagName.match(/input|select|textarea/i) || event.target.getAttribute('contenteditable')==="true") return;
 
    // We force a rescan of the page's images every time, for dynamic pages.
    positions = [];
    if (positions.length === 0) {
      //const images = document.images;
      const images = document.querySelectorAll('image, canvas, iframe');
      for (var index = 0; index < images.length; index++) {
        var image = images[index];
        if (image.clientWidth * image.clientHeight < 200*200) continue;
        var ytop = getYOffset(image);
        // Vertically centralise smaller images.
        if (image.clientHeight && image.clientHeight < window.innerHeight) {
          ytop -= (window.innerHeight - image.clientHeight)/2 | 0;
        }
        positions.push([index, ytop]);
      }
    }
    positions.sort(function(a,b) {
      return a[1] - b[1];
    });
 
    var scroll = Math.max(document.documentElement.scrollTop, document.body.scrollTop);
 
    if (code === forwardButton) {
      for (index = 0; index < positions.length; index++) {
        if (positions[index][1] <= scroll + leeway) continue;
        // Hard to detect which one our browser is using when we are at the top of the document.
        // Because Chrome presents documentElement.scrollTop = 0 all the time!
        // Likewise Firefox presents document.body.scrollTop = 0 all the time!
        // Solution?  Just set both of them!
        document.body.scrollTop = positions[index][1];
        document.documentElement.scrollTop = positions[index][1];
        return;
      }
    } else if (code === backwardButton) {
      for (index = positions.length - 1; index >= 0; index--) {
        if (positions[index][1] >= scroll - leeway) continue;
        document.body.scrollTop = positions[index][1];
        document.documentElement.scrollTop = positions[index][1];
        return;
      }
    }
 
  }, false);
 
  function getYOffset(node) {
    for (var offset = 0; node; offset += node.offsetTop, node = node.offsetParent);
    return offset;
  }
})();
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