Types of Errors in JavaScript

Errors are an inevitable part of programming, and JavaScript is no exception. Understanding the different types of errors and how to handle them can greatly improve your debugging skills and code quality. In this article, we’ll dive into the three main types of errors you might encounter in JavaScript: syntax errors, runtime errors, and logical errors.

1. Syntax Errors

Syntax errors occur when the code is written incorrectly according to the rules of the language. These errors are typically detected by the JavaScript engine during the parsing stage, before the code is actually executed.

Example:

function sayHello() {
  console.log("Hello, world!";
}

In the example above, there’s a syntax error due to the missing closing parenthesis. Syntax errors are usually easy to spot and fix because the JavaScript engine provides clear error messages indicating where the problem lies.

How to handle syntax errors:

• Carefully read the error message provided by the JavaScript engine.
• Check your code for typos or missing characters.
• Use a code editor with syntax highlighting and error checking.

2. Runtime Errors

Runtime errors, also known as exceptions, occur during the execution of the code. These errors happen when the code is syntactically correct but encounters an issue while running, such as trying to access a property of an undefined variable or attempting to divide by zero.

Example:

function divide(a, b) {
  return a / b;
}

console.log(divide(10, 0));

In the example above, the division by zero will result in a runtime error. Runtime errors can be harder to debug than syntax errors because they depend on the state of the program at a specific point in time.

How to handle runtime errors:

• Use try...catch blocks to handle exceptions gracefully.
• Validate inputs before performing operations.
• Use debugging tools to step through the code and inspect variables.

3. Logical Errors

Logical errors occur when the code runs without throwing any syntax or runtime errors, but it doesn’t produce the expected result. These errors are often the most difficult to detect because they don’t generate error messages. Logical errors arise from flaws in the program’s logic or incorrect assumptions made by the programmer.

Example:

function calculateTotal(price, tax) {
  return price - tax;
}

console.log(calculateTotal(100, 0.2)); // Expected output: 120, Actual output: 99.8

In the example above, there’s a logical error because the subtraction operator is used instead of the addition operator. The code runs without errors but produces the wrong result.

How to handle logical errors:

• Write test cases to validate your code’s behavior.
• Use console.log statements to trace the flow of your program and inspect variables.
• Perform code reviews and pair programming to catch logical errors early.