Variable declaration using let in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of let variable in block scope

What is the output of this code?

Javascript

let x = 10;
if (true) {
  let x = 20;
  console.log(x);
}
console.log(x);

A 20\n20

B 10\n20

C 20\n10

D 10\n10

💡 Hint

Remember that let variables are block scoped.

The variable x declared inside the if block is different from the one outside. Inside the block, x is 20, outside it remains 10.

❓ Predict Output

intermediate

Reassignment of let variable

What will be the output of this code?

Javascript

let count = 5;
count = 10;
console.log(count);

A 5

B 10

C undefined

D ReferenceError

💡 Hint

Variables declared with let can be reassigned.

The variable count is declared with let and then reassigned to 10, so the output is 10.

❓ Predict Output

advanced

Temporal Dead Zone with let

What error does this code produce?

Javascript

console.log(a);
let a = 3;

A ReferenceError

B SyntaxError

C TypeError

D undefined

💡 Hint

Variables declared with let are not hoisted like var.

Accessing a let variable before its declaration causes a ReferenceError due to the temporal dead zone.

❓ Predict Output

advanced

let in for loop scope

What is the output of this code?

Javascript

for (let i = 0; i < 3; i++) {
  setTimeout(() => console.log(i), 0);
}

A 0\n1\n2

B 3\n3\n3

C undefined\nundefined\nundefined

D 0\n0\n0

💡 Hint

Each iteration has its own block scope with let.

Using let in the loop creates a new i for each iteration, so the logged values are 0, 1, and 2.

🧠 Conceptual

expert

Why use let instead of var?

Which of the following is the main advantage of using let over var?

A <code>let</code> variables are hoisted and initialized with undefined.

B <code>let</code> variables can be redeclared in the same scope without errors.

C <code>let</code> variables are globally scoped by default.

D <code>let</code> variables are block scoped, preventing unexpected behavior in loops and conditionals.

💡 Hint

Think about how variable scope affects code reliability.

let is block scoped, which helps avoid bugs caused by var's function or global scope, especially in loops and conditionals.