Error chaining with the cause option

Wrapping low-level errors

When a low-level error happens deep in the stack, you usually want to add context before re-throwing — but you don't want to lose the original error. The { cause } option on Error does both:

async function loadProfile(userId) {
  try {
    return await db.findUser(userId);
  } catch (err) {
    throw new Error(\`failed to load profile for ${userId}\`, { cause: err });
  }
}

The caller catches the high-level error AND can drill into err.cause to inspect the original.

try {
  await loadProfile("u_123");
} catch (err) {
  console.error(err.message);        // "failed to load profile for u_123"
  console.error(err.cause?.message); // the underlying db error
}

Why not just re-throw?

Re-throwing keeps the message but loses the "where in the high-level flow did this happen" context. Wrapping adds business semantics; cause preserves the technical detail. Both layers stay available.

Stack vs cause

.stack shows where it was thrown. .cause shows what triggered it. Together they're invaluable in production logs.