How to remove delay from pop-up of chrome extension/Firefox add-on?

Question

I am building a bulk download extension from chrome and firefox to download a large number of files. The pop up of the extension has the cancel/pause/resume features. The pop up works fine when downloading a small number of files. However, when downloading a larger number of files, the pop-up menu takes forever to actually pop-up (or some time it doesn't whatsoever) probably because the extension becomes very busy and processing a lot of files at a time. Is there a way to eliminate this delay?

manifest.json

    "default_popup": "html/popup.html"
  },

popup.html

let bgPage = chrome.extension.getBackgroundPage(); //Getting the variables from the background page

let idsOfDownload = [];
idsOfDownload = bgPage.downloadIds;
console.log(idsOfDownload);

let cancel = document.createElement("button");
cancel.id = "cancel";
cancel.className = "btn";
cancel.innerHTML='<i class="fa fa-stop-circle"></i> Cancel All</button>';
document.body.appendChild(cancel);

$('body').width(350); 

setInterval(function(){

    let downloadString = LZString.decompress(localStorage.getItem('downloadLinks'));

    if(downloadString === "") return;

    let downloadLinks =  JSON.parse(downloadString);

    if (downloadLinks !== undefined && downloadLinks !== null && downloadLinks !== "null") {
        let status = `Total pending download: ${downloadLinks.length}`;
        jQuery("#download-status").html(status);
    }
},1000);


$(cancel).click(function () {
    chrome.runtime.sendMessage({message: "cancel-download"});
});

Answer 1

• Generally DOM is slow so if you have a lot of elements you should only display the visible stuff and draw the rest on demand when scrolling. There are many libraries and frameworks for this.

• LZString can be very slow with big strings so consider not using it or do it inside a web worker and pass the data via standard DOM messaging.

• window.localStorage is synchronous so it can be slow too if the data is big, consider switching to asynchronous storage like chrome.storage.local or IndexedDB.

Most importantly, use devtools profiler instead of guessing. After analyzing the results you'll see what needs fixing/rewriting. The popup has its own devtools (see how to open it).