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Introduction to Throwing Errors in JavaScript

When writing JavaScript applications, things don’t always go as expected. Users may enter invalid data, APIs may fail, or values may be missing. In such cases, JavaScript allows developers to manually throw errors to stop execution and handle problems properly.
Learning how to throw errors in JavaScript is an important step toward writing reliable and professional code.

What Does “Throwing an Error” Mean?

Throwing an error means intentionally creating an error in your code using the throw keyword. When an error is thrown:
  • JavaScript stops executing the current block
  • Control moves to the nearest catch block
  • If no catch exists, the program crashes
Basic Syntax of throw
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throw "Something went wrong";
You can throw:
  • Strings
  • Numbers
  • Objects
  • Built-in Error objects (recommended)
Throwing a Custom Error (Best Practice)
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throw new Error("Invalid input provided");
Using the Error object gives:
  • A readable message
  • Stack trace for debugging
  • Better error handling
Example: Validating User Input
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function checkAge(age) {
  if (age < 18) {
    throw new Error("Access denied: Age must be 18 or above");
  }
  return "Access granted";
}

try {
  console.log(checkAge(15));
} catch (error) {
  console.log(error.message);
}
This is a real-world example of throwing errors in JavaScript for input validation.

Throwing Errors with Different Types

Throwing a String (Not Recommended)
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throw "Invalid value";
Throwing an Object
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throw { message: "Custom error", code: 400 };
Throwing an Error Object (Recommended)
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throw new Error("Something failed");

Why Use throw in JavaScript?

Throwing errors helps you:
  • Stop invalid operations
  • Show meaningful messages
  • Prevent hidden bugs
  • Improve debugging
  • Create secure applications
This makes JavaScript throwing errors essential for modern web development.

throw with try...catch

Errors should always be handled using try…catch.
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try {
  throw new Error("Network error");
} catch (err) {
  console.log("Error caught:", err.message);
} finally {
  console.log("Execution completed");
}

Common Use Cases for Throwing Errors

  • Form validation
  • API response checking
  • Missing function parameters
  • Authentication failures
  • Business logic enforcement

Common Mistakes to Avoid

  • Throwing strings instead of Error objects
  • Not handling errors with try...catch
  • Showing technical messages to users
  • Ignoring error handling completely

Best Practices for Throwing Errors

  • Always throw Error objects
  • Write clear, user-friendly messages
  • Catch errors properly
  • Log errors for debugging
  • Do not expose sensitive data

Throw vs Console Error (Important Difference)

Feature throw console.error()
Stops execution ✔ Yes ❌ No
Triggers catch ✔ Yes ❌ No
Used for logic ✔ Yes ❌ No
Debugging only ❌ No ✔ Yes
JavaScript try…catch
JavaScript OOP