Why not just use promises?
side note: legit question, I don't do web/app dev
side note: legit question, I don't do web/app dev
So even if you put it behind a promise, when that promise actually runs, it will block the thread.
In essence, using promises (or callbacks or timeouts or anything else like that) allows you to delay the thread-blocking, but once the code hits `JSON.parse`, no other javascript will run until it completes. And since no other javascript will run, the UI is entirely unresponsive during that time as well.
[1] Technically there are web-workers, and I looked into them to try and solve this problem. Unfortunately any complex-objects that get sent to or from a worker need to be serialized (no pass-by-reference is allowed except for a very small subset of "C style" arrays called TypedArrays). So while you could technically send the string to a worker and have the worker call `JSON.parse` on it to get an object, when you go to pass that object back the javascript engine will need to do an "implicit" `JSON.stringify` in the worker, then a `JSON.parse` in the main thread. Making it entirely useless for my usecase.
But continuing with that same thought process, I very nearly went for an architecture that used a web-worker, did the `JSON.parse` in the worker, then exposed methods that could be called from the main thread to get small amounts of data out of the worker as needed. Something like `worker.getProperty('foo.bar.baz')` which would only take the parsing hit for very small subsets of the data at a time. But ultimately the oboe.js solution was simpler and faster at runtime.
I think of js entirely from a node.js perspective where I conceptualize it as an async task. Is this also wrong?
But both server-side and client-side JS use the same system, the event loop. It's basically a message-queue of events that get stacked up, and the JS engine will one at a time grab the oldest event in that queue and process it to completion. Anything "async" will just throw a new event into that queue of events to be processed. The secret sauce is that any IO is done "outside" the JS execution, so other events can be processed while the IO is waiting to complete.
Take a look at this link, or search up the JS event-loop if you want to get a better explanation. It's deceptively simple.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Even...
Yes, node.js javascript runtime is based on V8, the same that runs in Chrome. Javascript is single threaded so anything that is not I/O bound will block the main thread. If you don't want to block the thread becasue you have long running calculation/parsing task, then you can use worker threads[1]. This will run your task in separate thread and not block the main one.
[1] https://nodejs.org/dist/latest-v12.x/docs/api/worker_threads...
It's a really annoying problem, and I'm actually really happy to see that many others have the exact same thoughts I had at the time, and that I wasn't just missing something obvious!
For example: https://github.com/nodejs/node/blob/master/src/node_crypto.c...
I generally use that as an example when explaining to people why Node isn't a great fit for a lot of workloads. They have to use these features internally, but you as the user with a CPU-intensive job don't have access to those features.
If you have a large json object. You can use the fetch api to work with it. If you need to cache it, use the cache storage api. Unlike localStorage which will freeze the UI, cache storage wont.
It’s slightly slower since it needs to talk to another thread but who cares as long as the UI is responsive to do other things.
It looks like it doesn't, but the same exact symptoms will happen even while awaiting the fetch json().
http://oboejs.com/examples#demarshalling-json-to-an-oop-mode...
I could see the value in this for sure. I currently have a problem of loading a ton of JS for some users who have thousands of objects embedded in the view with Rails using toJSON() in a <script>. It’s creating far too much weight on the frontend. I’ve been considering fetching it via a simple REST request instead.
[0]: There is now the Web Workers API which does allow you to run code in the background. I've never used it, but I have heard that it has a pretty high overhead since you have to communicate with it through message passing, so it's possible you wouldn't actually gain anything by using it to parse a large JSON object.
https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers...
I believe you'd use Workers (WebWorkers?) https://developer.mozilla.org/en-US/docs/Web/API/Workers to actually do it off the main thread entirely inside JS.
You could try to use a web worker, but then you run into the problem that they don't have shared memory, so you need to pass data back some other way.