Even though async functions and the await operator quickly became popular in JavaScript, many use await solely with function calls, such as:

const result = await readSomeFile();

That works fine when you know the function you’re calling returns a promise. Actually, it works fine even without the function returning a promise as await will wrap the return value in a promise if it isn’t already one. But why go through the overhead of creating and returning a promise if it’s not needed?

The key here is that await operates on promises, and those are hidden when using await in front of a function call. Therefore, if you’re unsure that a function returns a promise, you can always check using the instanceof operator and only await if a promise is returned:

let result = someFunction();
if (result instanceof Promise) {
    result = await result;
}

The value of result is usable directly at the end of this code regardless if someFunction() returns a promise or not.