Real life examples of async function signatures in React + Typescript

#react #webdev #javascript #typescript

Async Function Returning a Boolean — A Practical Example

💡Intro

Theory is boring. Let’s check something real: is a user logged in? That’s a simple Boolean but in modern apps, it’s often async.

🧠Context

Sync version works if the info is instantly available.
But in practice, you check from a server or token → async.

Examples

// Synchronous
function isUserLoggedIn(): boolean {
  return true;
}

// Async
async function isUserLoggedIn(): Promise<boolean> {
  const response = await fetch("/api/check-login");
  const data = await response.json();
  return data.loggedIn;
}

// Arrow version
const isUserLoggedIn = async (): Promise<boolean> => {
  const response = await fetch("/api/check-login");
  const data = await response.json();
  return data.loggedIn;
};