Basic Reddit Content Exporter.js

// Basic Reddit Content Exporter
// Author: Dan Q <https://danq.me/>
// License: The Unlicense <https://unlicense.org/> / Public Domain

// 1. Go to www.reddit.com and log in (logging in means that we don't have to worry about a modhash)
// 2. Edit this script to include YOUR username and the content you want to download
// 3. Paste this script into your browser console
(()=>{
  const username = 'avapoet';  // <-- your username goes here (be sure to be logged in as it, too!)
  const content = 'submitted'; // <-- valid options: overview (everything), submitted (posts), comments,
                               //                    upvoted, downvoted, hidden, saved, gilded

  const limit = 100;           // <-- how many items to fetch at a time; 100 is the upper limit
  const rate = 2000;           // <-- milliseconds; the Reddit API requests that you make no more than
                               //     30 requests per minute so we take a 2000ms break between each
  const showProgress = true;   // <-- should progress be shown as-we-go-along or only at the end
                               //     (set to false to possibly maybe slightly improve performance)

  // Storage
  let data = []; 
  let after = '';

  // Set the page up so that we can use it for progress/output
  document.querySelectorAll('link, style').forEach(link=>link.remove()); // strip CSS
  const body = document.querySelector('body');
  body.innerHTML = `
    <h1>Basic Content Exporter</h1>
    <p>
      <label for="itemCounter">Items exported:</label>
      <input type="text" id="itemCounter" readonly />
      <span id="itemCounterStatus"></span>
    </p>
    <p>
      <label for="result">Output:</label>
      <textarea id="result" style="width: 100%; min-height: 80vh; resize: vertical;"></textarea>
    </p>
  `;
  const itemCounter = document.getElementById('itemCounter');
  const itemCounterStatus = document.getElementById('itemCounterStatus');
  const result = document.getElementById('result');

  // When all fetching is done, this function is called
  function allFetched(){
    if(!showProgress) result.value = JSON.stringify(data);
    itemCounterStatus.innerText = 'FINISHED!';
  }

  // Fetcher method pulls the next ${limit} (e.g. 100) entries and then queues another fetcher
  // if necessary or calls allFetched if not
  function fetcher(){
    const url = `https://www.reddit.com/user/${username}/${content}.json?limit=${limit}&after=${after}`;
    itemCounterStatus.innerText = `Fetching ${url}`;
    fetch(url, { credentials: 'include' }).then(r=>r.json()).then(json=>{
      // Merge new data in
      data = [...data, ...json.data.children];
      // Display progress
      if(showProgress) result.value = JSON.stringify(data);
      itemCounter.value = data.length;
      // Work out whether we're done yet
      if(json.data.after){
        // there's still more data to fetch!
        after = json.data.after;
        setTimeout(fetcher, rate);
        itemCounterStatus.innerText = `Waiting ${rate}ms`;
      } else {
        allFetched();
      }
    });
  }

  // Begin fetching!
  fetcher();
})();