JavaScript Interview Question #151

What is the difference between synchronous exceptions and Promise rejections?

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

Quick Interview Answer

A synchronous exception is thrown while ordinary JavaScript code is executing and can be caught by a surrounding synchronous try/catch. A Promise rejection represents failure of an asynchronous Promise operation and must be handled through await inside try/catch or with a rejection handler such as catch.

Detailed Explanation

A try/catch around code that merely starts a Promise does not automatically catch a rejection that occurs later unless that Promise is awaited inside the try block.

Code Example

try {
    const result = await loadData();
    console.log(result);
} catch (error) {
    console.error("Async failure:", error);
}

Promise.reject(new Error("Failed"))
    .catch(error => console.error(error));