JavaScript Error Handling Cheat Sheet

Covers try/catch/finally, custom Error subclasses, handling errors in promises and async/await, and the ES2022 error cause chain.

1 PageIntermediateApr 5, 2026

try/catch/finally Basics

Core syntax for catching and cleaning up after errors.

javascript

try {  const data = JSON.parse(input); // may throw SyntaxError  process(data);} catch (err) {  console.error('Failed:', err.message); // handle the error} finally {  cleanup(); // always runs, even after return/throw}// Optional catch binding (ES2019) - omit the error variabletry {  riskyOperation();} catch {  console.log('Something went wrong');}

Custom Error Classes

Extend Error to create typed, catchable error subclasses.

javascript

class ValidationError extends Error {  constructor(message, field) {    super(message);    this.name = 'ValidationError'; // shows up in stack traces    this.field = field;  }}function validate(age) {  if (age < 0) throw new ValidationError('Age cannot be negative', 'age');}try {  validate(-1);} catch (err) {  if (err instanceof ValidationError) {    console.log(`${err.field}: ${err.message}`);  }}

Errors in Promises & async/await

Handle rejections in async functions, promise chains, and globally.

javascript

// async/await - wrap in try/catchasync function loadUser(id) {  try {    const res = await fetch(`/api/users/${id}`);    if (!res.ok) throw new Error(`HTTP ${res.status}`);    return await res.json();  } catch (err) {    console.error('loadUser failed:', err);    throw err; // re-throw so callers can react too  }}// Promise chains - use .catch()fetchData()  .then(process)  .catch(err => console.error('Pipeline failed:', err));// Unhandled rejectionswindow.addEventListener('unhandledrejection', e => {  console.error('Unhandled:', e.reason);});

Built-in Error Types & Properties

Standard error constructors and the fields available on any error.

Error- Base error type; constructor accepts (message, options) where options.cause sets a chained cause
TypeError- Thrown when a value is not of the expected type, e.g. calling a non-function
RangeError- Thrown when a numeric value is outside its allowed range, e.g. invalid array length
SyntaxError- Thrown when parsing invalid JS or JSON.parse fails
ReferenceError- Thrown when referencing an undeclared variable
err.message- Human-readable description of the error
err.stack- Non-standard but widely supported stack trace string
err.cause- ES2022 option for chaining the underlying cause: new Error('msg', { cause: original })

Error Cause Chaining (ES2022)

Preserve the original error when wrapping it in a higher-level one.

javascript

try {  await connectToDb();} catch (dbErr) {  throw new Error('Failed to start server', { cause: dbErr }); // preserves original error}// Later, when logging:catch (err) {  console.error(err.message);  console.error('Caused by:', err.cause);}

Pro Tip

Always throw Error objects (or subclasses), never plain strings or objects - only Error instances capture a stack trace, and tools like Sentry rely on err.stack to be useful.

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