REPL for interactive exploration in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Node.js REPL code snippet?

Consider this code entered in the Node.js REPL. What will be the output after pressing Enter?

Node.js

const a = 5;
const b = 10;
a + b;

A 15

B undefined

C NaN

D SyntaxError

💡 Hint

Remember that the REPL evaluates expressions and shows their result.

In the Node.js REPL, expressions are evaluated and their result is printed. Here, a + b equals 15.

❓ component_behavior

intermediate

What happens when you declare a variable without var, let, or const in Node.js REPL?

In the Node.js REPL, what is the behavior of this code snippet? x = 42; x;

Node.js

x = 42;
x;

A SyntaxError

B ReferenceError: x is not defined

C undefined

D 42

💡 Hint

In REPL, assigning without declaration creates a global variable.

In the Node.js REPL, assigning a value to an undeclared variable creates a global variable. So x becomes 42.

📝 Syntax

advanced

Which option causes a SyntaxError in Node.js REPL?

Which of these code snippets will cause a SyntaxError when entered in the Node.js REPL?

A const x = ;

B function test() { return 1; }

C let y = 5;

D console.log('Hello');

💡 Hint

Look for incomplete or invalid syntax.

Option A has an incomplete variable declaration 'const x = ;' which is invalid syntax and causes a SyntaxError.

🔧 Debug

advanced

Why does this REPL code throw a ReferenceError?

In the Node.js REPL, why does this code throw a ReferenceError? console.log(myVar); let myVar = 10;

Node.js

console.log(myVar);
let myVar = 10;

A Because the REPL does not support let declarations

B Because console.log is not defined in REPL

C Because myVar is used before declaration and let does not hoist initialization

D Because myVar is declared with let and cannot be logged

💡 Hint

Think about variable hoisting and temporal dead zone.

Variables declared with let are hoisted but not initialized, so accessing them before declaration causes ReferenceError.

🧠 Conceptual

expert

What is the purpose of the underscore (_) variable in Node.js REPL?

In the Node.js REPL, what does the underscore (_) variable represent?

A It is used to clear the REPL screen

B It stores the result of the last evaluated expression

C It is a special variable for declaring constants

D It holds the current working directory path

💡 Hint

Try evaluating expressions and then typing _ to see what it holds.

The underscore variable in Node.js REPL automatically stores the value of the last expression evaluated.