Why is my infinite loop blocking when it is in an async function? [duplicate]

Question

This question already has an answer here:

• Proper way to write nonbloking function in node.js 1 answer

I don't understand how to work with asynchronous functions.

Why does the code below stop the main thread?

async function foo() {
  for (;;) {}
}
foo();

Answer 1

The async keyword doesn't make synchronous code asynchronous, slow running code fast, or blocking code non-blocking.

It just makes the function return a promise and provides (with the await keyword) a mechanism to interact with other promises as if there were synchronous.

Your function starts a loop, and then just goes around and around.

It doesn't get to the end of the function, which would end the function and resolve the promise it returned.

It doesn't reach an await keyword and pause while it waits for the awaited promise to be resolved.

It just goes around and around.

If you were actually doing something in the loop which was computationally expensive and you wanted to push off into the background, then you could use a Node.js Worker Thread or a browser-based Web Worker to do it.

Answer 2

Putting the async keyword before the function only implies that this is asynchronous function. You need to include the keyword await before the function that you want to actually wait for. Just like this:

async function hashPin(pin){
    const hashedPin = await bcrypt.hash(pin, saltRounds);
}

That's just the example from one of my projects (the redundant code has been removed before posting)