why is async keyword added in a node function while node is already asynchronous ? why we need to te-CodePudding

I want to know actual meaning of async keyword usage before function name in node js.

CodePudding user response：

Node.js is asynchronous in the idea that code does not need to run in the order it was called. However, you have to tell Node to do that for you.

Defining a function as async means that the function will return a Promise that resolves to whatever the return of the function is:

// This function returns a `Promise` that resolves to `true`
const func = async () => {
  return true;
}

Importantly, defining a function as async also allows the use of the await keyword:

const func = async () => {
  const result = await fetch("someUrl");
  return await result.toJSON();
}

async/await is just syntactic sugar for traditional Promises:

// This is the same function as above
const func = () => {
  return fetch("someUrl")
    .then(result => result.toJSON())
}

CodePudding user response：

An async function will ALWAYS return a promise. If it returns a non-promise, the return value will be wrapped in Promise.resolve. If it throws, it will wrap the exception in Promise.reject.

So the async keyword is a contract that guarantees the return value of the function to be asynchronus.

And this is required for the await keyword, because you can only await if you return a promise.