e621 Page Arrows

Change page on e621 using arrow keys

You will need to install an extension such as Tampermonkey, Greasemonkey or Violentmonkey to install this script.

You will need to install an extension such as Tampermonkey or Violentmonkey to install this script.

You will need to install an extension such as Tampermonkey or Violentmonkey to install this script.

You will need to install an extension such as Tampermonkey or Userscripts to install this script.

You will need to install an extension such as Tampermonkey to install this script.

You will need to install a user script manager extension to install this script.

(I already have a user script manager, let me install it!)

You will need to install an extension such as Stylus to install this style.

You will need to install an extension such as Stylus to install this style.

You will need to install an extension such as Stylus to install this style.

You will need to install a user style manager extension to install this style.

You will need to install a user style manager extension to install this style.

You will need to install a user style manager extension to install this style.

(I already have a user style manager, let me install it!)

// ==UserScript==
// @name         e621 Page Arrows
// @namespace    NA
// @version      0.2
// @description  Change page on e621 using arrow keys
// @author       kittywithclaws
// @include      https://e621.net/post/show/*
// @include      https://e621.net/post/index/*
// ==/UserScript==

//If it detects a Next or Previous button, add a keydown check.
//[Next >>] is used by Pool buttons, and [Next »] is used by the index. Mildly annoying inconsistent design.
var pool = false;
if(getElementsByText('Next >>').length!==0 || getElementsByText('<< Previous').length!==0){
    pool = true;
    document.body.onkeydown = function() {checkKeycode();};
}else if(getElementsByText('Next »').length!==0 || getElementsByText('« Previous').length!==0){
    document.body.onkeydown = function() {checkKeycode();};
}

//This skims the page for elements by text. Used to find Next/Prev buttons.
function getElementsByText(str, tag = 'a') {
  return Array.prototype.slice.call(document.getElementsByTagName(tag)).filter(el => el.textContent.trim() === str.trim());
}

function checkKeycode(event) {
    // handling Internet Explorer stupidity with window.event
    // @see http://stackoverflow.com/a/3985882/517705
    var keyDownEvent = event || window.event,
        keycode = (keyDownEvent.which) ? keyDownEvent.which : keyDownEvent.keyCode;

    //console.log(keycode);
    if(keycode==39 || keycode==37){
        changePage(keycode);
    }
    return false;
}
//Check if Left or Right arrow are pressed, and change page accordingly.
function changePage(keycode){
    if(keycode==39){
        //Right
        /*console.log(
            getElementsByText('Next >>')[0].href
        );*/
        if(pool){
            window.location.assign(getElementsByText('Next >>')[0].href);
        }else{
            window.location.assign(getElementsByText('Next »')[0].href);}
    }else if(keycode==37){
        //left
        /*console.log(
            getElementsByText('<< Previous')[0].href
        );*/
        if(pool){
            window.location.assign(getElementsByText('<< Previous')[0].href);
        }else{
            window.location.assign(getElementsByText('« Previous')[0].href);
        }
    }
}