Real life examples of async function signatures in React + 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; }; 

💡Real-Life Example:

Login checks in apps like Gmail, Slack, or banking dashboards, always asyncbecause they rely on tokens or API calls.

Even if you currently return true, keeping the function async future-proofs your code when you switch to an API.