Refactoring a thread image downloader bookmarklet to use 4chan's API instead of requiring 4chanX

4chan image downloader.js

/* Initialize this thread's variables */
let tp = window.location.pathname.split('/'),
    board = tp[1],
    threadNum = tp[3],
    jsonurl = `https://a.4cdn.org/${board}/thread/${threadNum}.json`,
    imho = `https://i.4cdn.org/${board}`,
    images = []; 

/* Get board JSON, populate images array */
await fetch(jsonurl)
  .then((response) => response.json())
  .then((data) => {
    for (post of data['posts']) {
      (typeof post['tim'] != 'undefined') && images.push({
        url: `${imho}/${post['tim']}${post['ext']}`, 
        filename: `${post['filename']}${post['ext']}`
      });
    }
});
/* await fetch(jsonurl)
  .then((response) => response.json())
  .then((data) => Object.keys(data['posts']).filter(([key]) => (key=='tim')));
  */
console.log(images);
function sleep(ms) {
  return new Promise(resolve => setInterval(resolve, ms));
}
/* retrieve files from images one second apart and download them using the original filenames */
// not having a fun time getting the function to actually wait instead of repeating the same download X number of times where X is the number of images
async function downloadImage(imageSrc, imageFilename) {
  let image = await fetch(imageSrc), 
      imageBlob = await image.blob(),
      imageURL = URL.createObjectURL(imageBlob),
      link = document.createElement('a');
  link.href = imageURL;
  link.download = imageFilename;
  sleep(2000).then(() => {document.body.appendChild(link); link.click(); document.body.removeChild(link);});
}
for (img of images) {  
  sleep(2000).then(() => {
    console.log(img['url'], img['filename']);
    downloadImage(img['url'], img['filename']);
  });
}
//let p=document.querySelectorAll("a.download-button"), i=0, 
//v=setInterval(() => {p[i++].click(); (i>p.length) && clearInterval(v);}, 1000);

Hardest part is remembering how to ensure a 1 second pause between downloads so that it doesn't hit 4chan's throttling and also so that it doesn't repeatedly download the first image in the array

The 'tim' key is the timestamp that only appears in posts with attachments; remove loop iteration checking each post for it to pack images, and try instead to use native object filters to reduce the JSON object to only posts with the 'tim' key in them. Still learning the syntax here.