Errors in JavaScript are problems that occur when the program cannot execute code as expected. Understanding errors helps in finding bugs quickly and writing stable, reliable applications. This guide explains what JavaScript errors are, common error types, why they happen, and how to handle them.

What Are Errors in JavaScript?

An error is an issue that stops normal execution of a program or causes incorrect behavior. Errors can happen due to wrong syntax, invalid operations, or unexpected values during runtime.

Common Types of JavaScript Errors

SyntaxError

Occurs when JavaScript code has invalid syntax.

JavaScript
1// Missing closing bracket
2if (true {
3 console.log("Hello");
4}

Explanation:
The program fails to run because the syntax is incorrect.

ReferenceError

Occurs when trying to use a variable that does not exist.

JavaScript
1console.log(value);

Explanation:
value is not defined, so JavaScript throws a reference error.

TypeError

Occurs when an operation is performed on an incompatible type.

JavaScript
1let num = 10;
2num();

Explanation:
A number is not a function, so calling it causes a type error.

RangeError

Occurs when a value is outside the allowed range.

JavaScript
1let arr = new Array(-1);

Explanation:
Array length cannot be negative, so a range error occurs.

Runtime Errors vs Compile-Time Errors

Error TypeWhen It HappensMeaning
SyntaxErrorBefore executionCode structure is wrong
Runtime ErrorsDuring executionCode runs but fails at runtime

Handling Errors with try...catch

JavaScript provides try...catch to handle runtime errors safely.

JavaScript
1try {
2 let result = JSON.parse("invalid");
3} catch (error) {
4 console.log("Parsing failed");
5}

Explanation:
The error is caught, and the program continues running.

Creating Custom Errors

JavaScript
1function withdraw(amount) {
2 if (amount <= 0) {
3 throw new Error("Invalid amount");
4 }
5}

Explanation:
throw creates a custom error with a message.

Common Causes of JavaScript Errors

  • Typing mistakes in code

  • Using variables before declaration

  • Calling methods on undefined or null values

  • Incorrect data types

  • Invalid user input

Basic Debugging Tips

  • Read error messages in the console

  • Check line numbers in stack traces

  • Use console.log() to inspect values

  • Test small parts of code

Summary

JavaScript errors help identify problems in code execution and logic. Common error types include SyntaxError, ReferenceError, TypeError, and RangeError. Using try...catch and proper debugging techniques allows handling errors safely and building stable JavaScript applications.