Persist javascript between pages

This is how to persist a piece of javascript code across pages in the browser. From time to time I read books in the browser (they’re old or not available yet) and I really hate that I have to touch the mouse to click a button like next or get out of the current directory and to the next file (git repos), something I found during my mouse battles was tampermonkey.

Tampermonkey is a free browser userscript manager.

A usecase example:

At the moment I am reading the “Learn C The Hard Way” by Zed A. Shaw, and I have to press the next or previous button when I want to go to the next or previous page.

Solution: Make a little script which emulates the user pressing click on that button whenever I press the right key (next page) or the left key (previous page).

First I need to know what tools I have so:

<script src="./javascripts/jquery.js"></script>

That means that I can select elements with $('element') and use .click function on that element. So selecting we do:

// Before I wrote the body like: document.body but it
// can't read arrow keys in chrome
const body = &('body');
const nextLink = document.getElementById('next_link');
const prevLink = document.getElementById('prev_link');

Then let’s write all our functionality in a self-executing function:

(function() {
  'use strict';
  const body = $('body');
  const nextLink = document.getElementById('next_link');
  const prevLink = document.getElementById('prev_link');
  body.keydown(key => {
    if (key.keyCode === 39) {
      nextLink.click(); // 39 coresponds to the right arrow key
    } else if (key.keyCode === 37) {
      prevLink.click(); // 37 to the left arrow key
    }
  })
})();

Now go to tampermonkey extension, press add new script and just add the code below the predefined comments.

Don’t forget to change the comments.

This code above is to be taken lightly. Every browser has it’s corner cases, I just made the code to work for my browser (chrome 50).

Add script, use script, be happy, read more! Don’sleep :)