JavaScript Runtime Semantics

Errors, Exceptions & Stack Traces

JavaScript can throw any value, but production code should throw Error objects or subclasses so stack traces, names, causes, and handling stay useful.

Thrown values interrupt normal control flow
Throw Error objects, not strings
Use cause to preserve lower-level failures
Async errors flow through Promises
Domain errors should be distinguishable

Custom domain error

class ValidationError extends Error {
  constructor(message, details) {
    super(message)
    this.name = "ValidationError"
    this.details = details
  }
}

try {
  saveUser(input)
} catch (err) {
  if (err instanceof ValidationError) {
    showFieldErrors(err.details)
  } else {
    throw err
  }
}

A domain-specific error lets callers handle expected failure differently from bugs.

Error handling choices
Pattern	Use for	Watch out
throw Error	Exceptional failure	Must be caught at boundary
Result object	Expected recoverable failure	Callers must check
Error subclass	Domain-specific handling	Keep inheritance simple
cause	Wrap lower-level error	Preserve original context