Truthiness narrowing in Typescript - Mini Project: Build & Apply

Truthiness Narrowing in TypeScript

📖 Scenario: You are building a simple program that checks user input values and decides if they are valid or not based on whether they are "truthy" or "falsy" in TypeScript.

🎯 Goal: Learn how to use truthiness narrowing to check if a variable has a meaningful value before using it.

📋 What You'll Learn

Create a variable with a value that can be truthy or falsy

Create a boolean variable to hold the check result

Use an if statement to narrow the type by checking truthiness

Print the result to the console

💡 Why This Matters

🌍 Real World

Checking if user inputs or data values exist before using them is common in web forms and applications.

💼 Career

Understanding truthiness narrowing helps avoid errors and write safer TypeScript code in real projects.

1

Create a variable with a value that can be truthy or falsy

Create a variable called userInput and assign it the value "Hello".

Typescript

# Create a variable called userInput and assign it the value "Hello"
// Your code here

Need a hint?

Use let userInput: string | null = "Hello"; to allow userInput to be a string or null.

2

Create a boolean variable to hold the check result

Create a boolean variable called isValid and set it to false.

Typescript

let userInput: string | null = "Hello";
// Create a boolean variable called isValid and set it to false
// Your code here

Need a hint?

Use let isValid: boolean = false; to create the boolean variable.

3

Use an if statement to narrow the type by checking truthiness

Use an if statement to check if userInput is truthy. Inside the if, set isValid to true.

Typescript

let userInput: string | null = "Hello";
let isValid: boolean = false;
// Use if statement to check if userInput is truthy
// Inside if, set isValid to true
// Your code here

Need a hint?

Use if (userInput) { isValid = true; } to check truthiness and update isValid.

4

Print the result to the console

Write a console.log statement to print the value of isValid.

Typescript

let userInput: string | null = "Hello";
let isValid: boolean = false;
if (userInput) {
    isValid = true;
}
// Print isValid to the console
// Your code here

Need a hint?

Use console.log(isValid); to show the result.