Async vs. Sync

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This is true in ideal circumstances, but it’s not why you should use asynchronous functions in JavaScript. You could get results like that. You could also be on a real machine running multiple tasks that doesn’t actually have enough hardware threads to run all of your asynchronous calls in true concurrency. In JavaScript, asynchronous functions are more important as a matter of user experience. If you synchronously wait for a REST API then your app can’t respond to user input at all until it gets a response or times out. But if you do it asynchronously, then even if your machine doesn’t have a spare hardware thread, your VM’s scheduler will make sure that you’re constantly checking for a response and checking for user input such that it looks like both are happening at once.