JavaScript

Errors are an inevitable part of programming, and JavaScript provides a variety of error types to help developers identify and debug issues effectively. Understanding how these errors work can significantly improve your ability to write and maintain code.

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1. What are JavaScript Errors?

JavaScript errors are problems that occur during the execution of code. These errors can stop script execution and usually result in a message being displayed in the console.

Errors are categorized into two main types:

• Syntax Errors: Occur when the code violates the syntax rules.
• Runtime Errors: Occur while the program is running.

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2. Common Types of JavaScript Errors

a. SyntaxError

Occurs when code is written incorrectly and doesn’t follow JavaScript syntax.

console.log("Hello); // Missing closing quote

Error: Unexpected end of input

b. ReferenceError

Occurs when a non-existent variable is referenced.

console.log(userName); // userName is not defined

c. TypeError

Occurs when a value is not of the expected type.

let num = 5;
num.toUpperCase(); // toUpperCase is not a function for numbers

d. RangeError

Occurs when a value is not within the set or allowed range.

let num = new Array(-1); // Invalid array length

e. EvalError

Thrown when the eval() function is used incorrectly (rare in modern JS).

f. URIError

Occurs when global URI handling functions are used incorrectly.

decodeURIComponent('%'); // Malformed URI sequence

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3. Custom Errors with throw

You can create your own errors using the throw keyword.

throw new Error("Something went wrong!");

You can also define specific error types:

throw new TypeError("Invalid type!");

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4. Handling Errors with try…catch

JavaScript allows you to handle errors gracefully using try...catch blocks.

try {
  let result = riskyOperation();
} catch (error) {
  console.error("Error occurred:", error.message);
}

You can also use finally for code that must execute regardless of error:

try {
  // Code that may throw an error
} catch (err) {
  // Handle error
} finally {
  // Always executed
}

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5. Debugging Tips

• Use browser developer tools (Chrome DevTools, Firefox Debugger).
• Use console.log() generously during development.
• Read the full stack trace for understanding where the error occurred.
• Make use of linters (like ESLint) to catch errors early.

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6. Conclusion

JavaScript errors are valuable tools that help us understand what went wrong in our code. By learning how to identify, throw, and handle errors, developers can write more resilient and maintainable applications. Make sure to embrace errors and use them as learning opportunities.