Do Async Functions Always Return Promises?

Question: Do Async Functions Implicitly Return Promises?

In JavaScript, async functions are declared using the async keyword and are frequently thought to automatically return promises. However, this raises a potential inconsistency: when a non-promise value is explicitly returned, the function appears to wrap the value in a promise.

Answer: All Async Functions Return Promises

The behavior observed is correct: all async functions implicitly return promises. Specifically:

• When an async function returns without an explicit return statement, it returns a promise resolved to undefined.
• When an async function explicitly returns a non-promise value, it wraps the value in a promise resolved to that value.
• Even when an async function contains an await expression, the returned value is still a promise, wrapping the result of the await expression.
• If an error is thrown inside an async function, the returned promise is rejected with that error.

Example:

async function increment(num) {
  return num + 1;
}

// Logs 4, as the returned promise resolves to 4.
increment(3).then(num => console.log(num));

Wrapping Behavior:

This wrapping behavior is unique to generator functions. For instance, generator functions also return promises, but in a different manner:

function* foo() {
  return 'test';
}

// Logs an object, not "test".
console.log(foo());

// Logs 'test' by explicitly calling .next() on the generator function.
console.log(foo().next().value);

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