JavaScript How to know if a function returns a promise

To know if a function returns a promise or not, there are a few ways to check if a function returns a promise:

A. Check the Return Type:

You can check the return value of a function at runtime using instanceof. If the function returns a promise, it should be an instance of the Promise class:

function exampleFunction() {
  return new Promise((resolve, reject) => {
    resolve('Success!');
  });
}

const result = exampleFunction();
console.log(result instanceof Promise);  // true if it's a promise
Inspect the Function’s Documentation:

Many JavaScript APIs (like fetch or async functions) are documented to indicate that they return promises. Checking the documentation is often the quickest way to confirm if a function returns a promise.

B. Look for async Functions:

If a function is declared with the async keyword, it automatically returns a promise. So if you see async function, you know it’s returning a promise.