Running TypeScript with ts-node - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output when running this TypeScript code with ts-node?

Consider the following TypeScript code snippet. What will be printed to the console when you run it using ts-node?

Typescript

const greet = (name: string): string => {
  return `Hello, ${name}!`;
};

console.log(greet("Alice"));

A Hello, Alice!

B greet is not defined

C Hello, undefined!

D SyntaxError: Unexpected token

💡 Hint

Think about how arrow functions and template strings work in TypeScript and JavaScript.

The function greet takes a string and returns a greeting using a template string. When run with ts-node, it compiles and executes correctly, printing Hello, Alice!.

🧠 Conceptual

intermediate

Which command runs a TypeScript file directly using ts-node?

You want to run a TypeScript file named app.ts without compiling it first. Which command should you use?

A npm run app.ts

B node app.ts

C tsc app.ts && node app.js

D ts-node app.ts

💡 Hint

Remember, ts-node runs TypeScript files directly without manual compilation.

The ts-node command runs TypeScript files directly. Using node app.ts will fail because Node.js does not understand TypeScript syntax. Option D compiles then runs but is not direct. Option D is not a valid npm command.

🔧 Debug

advanced

What error occurs when running this code with ts-node?

Look at this TypeScript code. When run with ts-node, what error will it produce?

Typescript

function add(a: number, b: number): number {
  return a + b;
}

console.log(add(5, "3"));

A SyntaxError: Unexpected string

B Argument of type 'string' is not assignable to parameter of type 'number'

C No error, output is 8

D TypeError: Cannot add number and string

💡 Hint

Think about TypeScript's type checking during execution with ts-node.

TypeScript checks types at compile time, but ts-node performs compilation and execution together. Passing a string where a number is expected causes a type error: Argument of type 'string' is not assignable to parameter of type 'number'.

📝 Syntax

advanced

Which option causes a syntax error when run with ts-node?

Identify which code snippet will cause a syntax error when executed with ts-node.

A

const z: string = 'hello
console.log(z);

B

const x: number = 10;
console.log(x);

C

function foo() { return 42; }
console.log(foo());

D

let y = 5
console.log(y);

💡 Hint

Look carefully at string literals and missing characters.

Option A has a missing closing quote for the string, causing a syntax error. Other options are syntactically correct.

🚀 Application

expert

How many items are in the resulting array after running this code with ts-node?

Consider this TypeScript code run with ts-node. How many elements does the result array contain?

Typescript

const numbers = [1, 2, 3, 4, 5];
const result = numbers.map(n => {
  if (n % 2 === 0) {
    return n * 2;
  }
});
console.log(result);

A 0

B 3

C 5

D 2

💡 Hint

Remember how map works and what happens when a function returns undefined.

The map method returns an array of the same length as the original. For odd numbers, the function returns undefined. So result has 5 elements, some are numbers, some are undefined.