Hoisting with let and const in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code snippet?

Consider the following JavaScript code:

console.log(a);
let a = 5;

What will be printed to the console?

Javascript

console.log(a);
let a = 5;

A null

B ReferenceError

C 5

D undefined

💡 Hint

Think about the temporal dead zone for let variables.

Variables declared with let are hoisted but not initialized. Accessing them before declaration causes a ReferenceError due to the temporal dead zone.

❓ Predict Output

intermediate

What is the output of this code snippet?

Look at this code:

console.log(b);
const b = 10;

What will be the output?

Javascript

console.log(b);
const b = 10;

A 10

B TypeError

C undefined

D ReferenceError

💡 Hint

Remember how const variables behave before initialization.

const variables are hoisted but not initialized. Accessing them before declaration causes a ReferenceError due to the temporal dead zone.

❓ Predict Output

advanced

What is the output of this code snippet?

Analyze this code:

var x = 1;
{
  console.log(x);
  let x = 2;
}

What will be printed?

Javascript

var x = 1;
{
  console.log(x);
  let x = 2;
}

A ReferenceError

B 2

C 1

D undefined

💡 Hint

Consider the block scope and temporal dead zone of let.

The block declares a new let x which shadows the outer var x. The console.log(x) tries to access the inner x before initialization, causing a ReferenceError.

❓ Predict Output

advanced

What is the output of this code snippet?

Consider this code:

function test() {
  console.log(y);
  const y = 3;
}
test();

What will be printed when test() is called?

Javascript

function test() {
  console.log(y);
  const y = 3;
}
test();

A ReferenceError

B undefined

C 3

D TypeError

💡 Hint

Think about the temporal dead zone inside functions with const.

The variable y is declared with const inside the function. Accessing it before declaration causes a ReferenceError due to the temporal dead zone.

🧠 Conceptual

expert

Which option correctly explains hoisting behavior of let and const?

Choose the statement that best describes how let and const variables behave during hoisting in JavaScript.

A <p><code>let</code> and <code>const</code> variables are hoisted and initialized with <code>undefined</code> before code execution.</p>

B <p><code>let</code> variables are hoisted and initialized, but <code>const</code> variables are not hoisted at all.</p>

C <p><code>let</code> and <code>const</code> variables are hoisted but not initialized, causing a temporal dead zone until their declaration is reached.</p>

D <p><code>let</code> and <code>const</code> variables behave exactly like <code>var</code> during hoisting.</p>

💡 Hint

Recall the temporal dead zone concept for let and const.

Both let and const declarations are hoisted but remain uninitialized until their declaration line is executed. Accessing them before initialization causes a temporal dead zone error.