Why use async/await, it makes code work like sync-CodePudding

If you use promise's then() syntax, you can truly run codes concurrently.

See this example.

async function asyncFunc() {
  return '2';
}

console.log('1')
asyncFunc().then(result => console.log(result))
console.log('3')

this prints 1 -> 3 -> 2 because asyncFunction() runs in "async" and rest of code ('3') runs without delay.

But if you use async/await syntax, doesn't it work like plain ordinary "sync" code?

async function asyncFunc() {
  return '2';
}

console.log('1')
const result = await asyncFunc()
console.log(result)
console.log('3')

this would print 1->2->3 because it "defers" rest of the code to "await" asyncFunction()

So I'm curious about the purpose of async/await syntax. I guess it allows you to use async functions like sync function. With async/await, I can easily see how my code runs because it has the same flow as plain sync code. But then, why not just use sync code in the first place?

But I'm sure I'm missing something here right? What is the purpose of async/await syntax?

CodePudding user response：

The idea of async/await is as follows:

It is a syntactic sugar for promises. It allows to use async code (like Web Api's - AJAX, DOM api's etc.) in synchronous order.

You ask "But then, why not just use sync code in the first place?" - because in your example you forced a sync code to be returned in a promise, basically you made it async, but it could run as sync in the first place, but there are Web APIs as mentioned above, that work ONLY ASYNC (meaning you have to wait for them to be executed), that's why you cannot turn them in sync "in the first place" :)

When JavaScript encounters the await expression, it pauses the async function execution and waits until the promise is fulfilled (the promise successfully resolved) or rejected (an error has occurred), then it continues the execution where it pauses in that function... The promise can be code from JS engine (as in your case) or it can be from another place like browser apis (truly async).