JavaScript Interview Question #152

What is an unhandled Promise rejection?

Performance, Browser APIs, Rendering & Modern Web Architecture Senior Advanced

Quick Interview Answer

An unhandled Promise rejection occurs when a Promise rejects and the application does not attach an appropriate rejection handler within the runtime's handling rules. In browsers and server runtimes this can produce warnings, diagnostic events, or process-level consequences depending on the environment.

Detailed Explanation

Production code should deliberately handle expected failures and allow unexpected failures to reach a centralized logging or error boundary rather than silently ignoring them.

Code Example

async function load() {
    throw new Error("Request failed");
}

// Bad if nobody handles the returned Promise:
// load();

// Better:
load().catch(error => {
    console.error("Load failed:", error);
});