Error Types

Types of Errors

JavaScript has several built-in error types. Understanding them helps you write better error handling and debug faster. Each error type has a specific name that tells you what went wrong.

// ReferenceError — using a variable that doesn't exists
console.log(x); // ReferenceError: x is not defined

// TypeError — wrong type of operation
null.foo(); // TypeError: Cannot read properties of null

// SyntaxError — code that can't be parsed
eval("function("); // SyntaxError

// RangeError — value outside allowed range
const arr = new Array(-1); // RangeError

// URIError — malformed URI
decodeURI("%"); // URIError

Catching Specific Errors

You can check the error type inside a catch block and handle each one differently.

try {
  JSON.parse("not json");
} catch (error) {
  if (error instanceof SyntaxError) {
    console.log("Invalid JSON format");
  } else {
    console.log("Something else went wrong");
  }
}

Creating Custom Error Types

You can extend the built-in Error class to create your own error types. This makes your code more readable and easier to debug.

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

function validateAge(age) {
  if (age < 0 || age > 150) {
    throw new ValidationError("Invalid age", "age");
  }
}

Error Properties

Every error object has useful properties like name, message, and stack. The stack trace shows you exactly where the error occurred.

try {
  undefinedFunction();
} catch (error) {
  console.log(error.name);    // "ReferenceError"
  console.log(error.message); // "undefinedFunction is not defined"
  console.log(error.stack);   // Full stack trace
}

Summary

Knowing the different error types helps you handle errors gracefully. Use instanceof to check error types, and create custom error classes for domain-specific validation.