Throwing errors in Javascript - Mini Project: Build & Apply

Throwing errors

📖 Scenario: Imagine you are making a simple calculator app. You want to make sure users only enter numbers when they try to add two values. If they enter something else, you want to show a clear error message.

🎯 Goal: You will build a small program that checks if inputs are numbers. If not, it will throw an error with a helpful message.

📋 What You'll Learn

Create two variables with exact names and values

Create a helper variable to check input types

Use throw new Error() to raise an error if inputs are not numbers

Print the result or error message

💡 Why This Matters

🌍 Real World

Throwing errors helps programs stop when something goes wrong, so users get clear messages instead of confusing results.

💼 Career

Understanding error handling is important for writing reliable code and debugging in real software projects.

1

Create input variables

Create two variables called input1 and input2. Set input1 to the number 10 and input2 to the string "five".

Javascript

// Create variables input1 and input2 with the exact values
// Your code here

Need a hint?

Use const to create variables. Remember to put quotes around strings.

2

Create a helper variable to check types

Create a variable called areNumbers that is true only if both input1 and input2 are numbers. Use the typeof operator to check each input.

Javascript

const input1 = 10;
const input2 = "five";
// Create variable areNumbers to check if input1 and input2 are numbers
// Your code here

Need a hint?

Use typeof input1 === "number" and combine with && for both inputs.

3

Throw an error if inputs are not numbers

Write an if statement that checks if areNumbers is false. Inside the if, throw a new error with the message "Both inputs must be numbers". Otherwise, create a variable sum that adds input1 and input2.

Javascript

const input1 = 10;
const input2 = "five";
const areNumbers = typeof input1 === "number" && typeof input2 === "number";
// Use if statement to throw error if areNumbers is false
// Otherwise, create sum = input1 + input2
// Your code here

Need a hint?

Use throw new Error("message") inside the if block.

4

Print the result or catch the error

Wrap the previous code in a try block. In the try, calculate the sum as before. In the catch block, print the error message using console.log(error.message). If no error, print the sum with console.log(sum).

Javascript

const input1 = 10;
const input2 = "five";
const areNumbers = typeof input1 === "number" && typeof input2 === "number";
// Wrap code in try-catch
// Print sum if no error, else print error.message
// Your code here

Need a hint?

Use try { ... } catch (error) { ... } to handle errors and print messages.