js/throw-error-objects

Why

A thrown string has no stack trace, no name and no cause, so the error report says only "Uncaught Load failed" with no file or line. Code that catches it cannot tell it apart with instanceof, and error.message is undefined.

Fix

throw new Error('Load failed', { cause: err }), or a subclass (class HttpError extends Error) when callers need to tell errors apart. Reject promises with Error objects as well.

Examples

// bad
if (!res.ok) throw 'Load failed'
return Promise.reject({ code: 404 })
// good
if (!res.ok) throw new HttpError(res.status, 'Load failed')
return Promise.reject(new HttpError(404, 'Not found'))

Sources

• MDN, throw (throwing an object)
• ESLint, no-throw-literal

Read it in the terminal

npx github:dawidolko/frontend-skills explain js/throw-error-objects