Robust error handling separates production-ready developers from tutorial-level code. Interviews cover sync errors, Promise rejections, and global handlers.
Common Interview Questions
Q: Does try/catch catch async errors in async functions?
Answer: Yes, if you await inside try/catch — rejected Promises become catchable exceptions. Without await, a .then rejection bypasses surrounding try/catch.
async function load() {
try {
const data = await fetch("/api");
if (!data.ok) throw new Error("HTTP " + data.status);
} catch (err) {
console.error(err);
}
}
Q: What is the difference between Error and thrown strings?
Answer: Always throw Error objects (or subclasses) for stack traces and consistent handling. Throwing strings loses debugging context.
Q: Custom error classes?
Answer: Subclass Error, set name, and attach metadata. Use instanceof or error codes for branching in API layers.
class ValidationError extends Error {
constructor(message, field) {
super(message);
this.name = "ValidationError";
this.field = field;
}
}
Q: Unhandled promise rejection?
Answer: Node and browsers emit unhandledrejection events. Always .catch() or try/catch awaited promises. In Node 15+, unhandled rejections can crash the process.
Key Points for Interviews
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Prefer Error objects with meaningful messages
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Async errors need await inside try/catch
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finally runs regardless of success or failure
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Distinguish operational vs programmer errors in APIs
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Global handlers are last resort, not primary strategy