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I'm very new to JavaScript, please bear with me if this is quite obvious.

I was watching this video about the event queue and I wrote this code segment to try and see if I understood how JavaScript queues asynchronous functions into their section (I'm not sure what it's called. In the video, it called it a webapi).

setTimeout( () => console.log('hello'), 5000);
setTimeout( () => console.log('123'), 5000);

From my understanding, the first line of code gets sent off to a separate thread where it starts to get evaluated. Then, the second line of code gets sent off to another thread (different from the first) to get evaluated. As each of these evaluations complete in their own separate threads, they will eventually call their callback function, adding it to the task queue, where the event loop will push them back into the main stack.

I'm hoping someone can confirm or correct me on this, and would appreciate any further reading to help solidify this idea. I have to admit, when I first started reading about asynch functions, I was puzzled since I thought JavaScript was single threaded (so how could it yield any benefits?). I know, foolish.

Phil
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articuno
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    Not separate threads. – Pointy May 04 '22 at 01:51
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    No, JS is single-threaded. First line of code runs, queues a task, then finishes. Second line of code runs, queues a task, then finishes. – CertainPerformance May 04 '22 at 01:52
  • for a start, javascript being "single threaded" is a misnomer, threads are irrelevant. secondly, the Javascript Engine itself (the thing that "runs" the javascript) can have as many "threads" as it needs, and that doesn't effect how your javascript code is executed – Bravo May 04 '22 at 01:54
  • @CertainPerformance So when you have asynchronous functions, wouldn't they become blocking? I'm a bit confused here. – articuno May 04 '22 at 01:55
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    No, they would not - I haven't found a better explanation about this apparent contradiction - I look at it like in my first comment ... your javscript code is so-called "single threaded" in that only one statement is executed at any time, single call stack etc etc other things that define "single threaded" ... but there's an underlying engine that interprets the JS code, and it is NOT single threaded, it can make networks requests, and wait for timeouts etc, and manipulate your codes event queue as appropriate ... since javascript is *event driven*, it's the event queue that drives everything – Bravo May 04 '22 at 02:05
  • Ohh I see, thanks you for the explanation @Bravo, appreciate it! – articuno May 04 '22 at 02:23

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