node.js - Please point out the misfacts in my learning regarding Asynchronous Javascript

Question

I am new to Javascript and Ascynchronous programming, and a few things confuse me, please point out the misfacts in my learning.

• Callbacks of an Asynchronous function are put in a message queue and executed via event loop.
• Asynchronous execution is non-blocking, done via event loop.
• Functions like setTimeout are asynchronous.
• Asynchronous functions are blocking, only their callbacks are non-blocking.

If any of the above are wrong, please elaborate it.

Answer 1

Callbacks of an Asynchronous function are put in a message queue and executed via event loop.

No.

There are generally two kinds of asynchronous functions - ones that take some sort of callback to run when they are done and ones that produce a Promise as a result.

Callback-based functions

This is an example of a callback-based function:

setTimeout(() => console.log("foo"), 0);

console.log("bar");

/* output: 
bar
foo
*/