Update object stored in chrome extension's local storage

Question

I'm developing a chrome extension and I will store objects sent by server. For example, I will receive:

command = {id:"1", type: "A", size: "B", priority: "C"}

If I had a database, I would insert it as a line in table commands. Using chrome.storage, I'm storing an array of these object in key commands.

But, when I receive a new command by server, I have to get from local storage, update the array and then set again. I'm worried about cases when I receive another command while I'm getting and setting or while I delete a stored command. I'm thinking about semaphores, but I don't know if it's a great idea.

Can someone suggest me what to do?

thanks!

Answer 1

Extensions can use a database: IndexedDB (the sample code may look convoluted, but it's pretty simple in the actual extensions, for example two small functions here, getStyles and saveStyle, or IDB-keyval wrapper library).

If you want to use chrome.storage, just maintain a global queue array that is populated by the server listener:

queue.push(newItem);
updateStorage();

and processed in chrome.storage.local.get callback:

function updateStorage() {
    if (!queue.length) {
        return;
    }
    chrome.storage.local.get('commands', function(data) {
        data.commands = [].concat(data.commands || [], queue);
        queue = [];
        chrome.storage.local.set(data);
    });
}

As Javascript engine is single-threaded, there's no need to worry queue might be changed while chrome.storage.local.get runs.