How to Throw Error in JavaScript: Syntax and Examples

In JavaScript, you throw an error using the throw statement followed by an Error object or any value. For example, throw new Error('message') stops execution and signals an error.

Syntax

The throw statement is used to create a custom error. You write throw followed by an Error object or any value you want to signal as an error.

• throw: keyword to raise an error
• new Error('message'): creates an error object with a message

javascript

throw new Error('This is an error message');

Example

This example shows how to throw an error inside a function when a condition is not met. The error stops the program and shows the message.

javascript

function checkAge(age) {
  if (age < 18) {
    throw new Error('Age must be 18 or older');
  }
  return 'Access granted';
}

try {
  console.log(checkAge(16));
} catch (error) {
  console.log('Error caught:', error.message);
}

Output

Error caught: Age must be 18 or older

Common Pitfalls

Common mistakes include throwing strings instead of Error objects, which makes debugging harder, and forgetting to catch errors, causing the program to crash.

javascript

/* Wrong way: throwing a string */
// throw 'This is an error';

/* Right way: throwing an Error object */
throw new Error('This is an error');

Quick Reference

Action	Syntax Example
Throw a new error	throw new Error('message');
Throw a custom error type	throw new TypeError('wrong type');
Throw a string (not recommended)	throw 'error message';
Catch an error	try { /* code */ } catch (e) { /* handle error */ }

Key Takeaways

Use throw new Error('message') to raise errors clearly.

Always throw Error objects, not strings, for better debugging.

Use try...catch blocks to handle thrown errors safely.

Throwing an error stops normal code execution immediately.

Custom error types like TypeError can clarify error causes.