throw Statement

🤮 Throw Statement in Action

The throw statement is used to manually create (or throw) an error in JavaScript.

You can throw custom errors using throw, and it will immediately stop the execution of code in the current block and transfer control to the nearest catch block.

You can throw:

• Error object: throw new Error("message")

• A string: throw "Something went wrong"

• A number, boolean, object, etc.

• An instance of Error, TypeError, ReferenceError, etc. (✅ recommended)

This is useful when:

• You want to stop the execution under invalid conditions

• You want to signal an error condition

• You want to customize error messages

🔧 Syntax

throw expression;

🐞 Throwing a String (Not recommended for large apps)

try {
  throw "Something went wrong!";
} catch (err) {
  console.log("Caught error:", err);
}

Caught error: Something went wrong!

🔴 Drawback: err is just a string — it doesn't have name, message, or stack trace.

🐛 Throwing a Built-in Error Object (Recommended)

try {
  throw new Error("Invalid operation");
} catch (err) {
  console.log("Error name:", err.name);      // Error
  console.log("Error message:", err.message); // Invalid operation
}

Error name: Error
Error message: Invalid operation

🧠 Using Error gives access to:

• .name

• .message

• .stack (useful for debugging)

📚 Types of Built-in Error Objects You Can Throw

JavaScript has built-in error types like:

function divide(a, b) {
  if (typeof a !== "number" || typeof b !== "number") {
    throw new TypeError("Both arguments must be numbers.");
  }
  return a / b;
}

try {
  divide("10", 2);
} catch (err) {
  console.log("Caught:", err.name);    // TypeError
  console.log("Message:", err.message); // Both arguments must be numbers.
}

Caught: TypeError
Message: Both arguments must be numbers

function validateAge(age) {
  if (age < 0) {
    throw new RangeError("Age cannot be negative");
  }
  console.log("Age is valid:", age);
}

try {
  validateAge(-5);
} catch (error) {
  console.log("🚫 Error Type:", error.name);     // RangeError
  console.log("📩 Message:", error.message);     // Age cannot be negative
}

🚫 Error Type: RangeError
📩 Message: Age cannot be negative

🔄 Execution Flow with throw

function test() {
  console.log("Before throw");
  throw new Error("Something broke");
  console.log("After throw"); // ❌ Never runs
}

try {
  test();
} catch (e) {
  console.log("Caught:", e.message);
}

Before throw
Caught: Something broke

🔥 Once throw is executed, control immediately jumps to the nearest catch block, and the remaining code in the try block is skipped.

✅ Best Practices