Combining try…catch with Custom Errors

Custom errors and specific error types help create more meaningful error messages and workflows for users.

Example: User Login with Error Handling

Let’s say you’re validating a user’s login. You want to catch errors if the username or password is missing.

JavaScript
function loginUser(username, password) {
  try {
    if (!username) throw new ReferenceError("Username is required.");
    if (!password) throw new ReferenceError("Password is required.");
    if (password.length < 8) throw new Error("Password must be at least 8 characters.");

    console.log("Login successful!");
  } catch (error) {
    console.log("Login Error:", error.message);
  }
}

loginUser("", "");                // Login Error: Username is required.
loginUser("user", "pass");        // Login Error: Password must be at least 8 characters.
loginUser("user", "securepass");  // Login successful!

This example uses custom errors and ReferenceError for missing fields and checks for password length. This way, users get clear feedback about why login fails.

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