throw and catch — the basic shape

throw stops execution

throw expression aborts the current function and walks up the call stack until a catch block grabs it. Anything is throwable, but you should throw Error objects — they carry a stack trace.

function parseAge(s) {
  const n = Number(s);
  if (Number.isNaN(n)) throw new Error("not a number: " + s);
  if (n < 0)           throw new Error("age cannot be negative: " + n);
  return n;
}

try {
  parseAge("forty");
} catch (err) {
  console.log("caught:", err.message); // caught: not a number: forty
}

The contract

• try — code that might throw.
• catch (err) — runs only if try threw. err is whatever was thrown.
• The catch parameter can be untyped (catch (err)) — TypeScript-aware editors treat it as unknown until you narrow.

Don't throw strings

throw "broken" works syntactically but loses the stack trace and breaks tooling. Always throw new Error("broken").