Variable declaration using let in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable named age using let.

Javascript

[1] age = 25;

Drag options to blanks, or click blank then click option'

Alet

Bvar

Cconst

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using var instead of let.

Using const which does not allow reassignment.

Using non-JavaScript keywords like int.

Use let to declare a variable that can change later.

2fill in blank

medium

Complete the code to declare a variable name and assign it the string 'Alice' using let.

Javascript

[1] name = 'Alice';

Drag options to blanks, or click blank then click option'

Aconst

Blet

Cfunction

Dvar

Attempts:

3 left

💡 Hint

Common Mistakes

Using const which prevents reassignment.

Using function which is not for variable declaration.

let declares a variable that can be changed later. Here, name is assigned the string 'Alice'.

3fill in blank

hard

Fix the error by completing the code to declare a variable count with let.

Javascript

let [1] = 10;

Drag options to blanks, or click blank then click option'

Alet

B10

Cvar

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number as a variable name.

Using keywords as variable names.

The variable name should be count. The keyword let is already used.

4fill in blank

hard

Fill both blanks to declare two variables x and y using let and assign them values 5 and 10.

Javascript

[1] x = 5; [2] y = 10;

Drag options to blanks, or click blank then click option'

Alet

Bconst

Dvar

Attempts:

3 left

💡 Hint

Common Mistakes

Using const which prevents reassignment.

Using var instead of let.

Use let before each variable to declare them properly.

5fill in blank

hard

Fill all three blanks to declare variables a, b, and c using let and assign them values 1, 2, and 3 respectively.

Javascript

[1] a = 1; [2] b = 2; [3] c = 3;

Drag options to blanks, or click blank then click option'

Alet

Bconst

Cvar

Attempts:

3 left

💡 Hint

Common Mistakes

Using const which prevents reassignment.

Using var instead of let.

Each variable is declared with let. The order of let keywords matches the blanks.

Practice

1. What does the let keyword do in JavaScript?

easy

A. Declares a constant variable that cannot change

B. Declares a variable that can change value and has block scope

C. Declares a variable with global scope only

D. Declares a function

Solution

1. Step 1: Understand let behavior

   let declares variables that can be reassigned new values.

2. Step 2: Understand scope of let

   Variables declared with let are limited to the block they are declared in (block scope).

3. Final Answer:

   Declares a variable that can change value and has block scope -> Option B

4. Quick Check:

   let = variable with block scope [OK]

Hint: Remember: let = changeable variable inside blocks [OK]

Common Mistakes:

• Confusing let with const (constant)
• Thinking let variables have global scope
• Mixing let with function declarations

2. Which of the following is the correct syntax to declare a variable named score using let?

easy

A. let = score 10;

B. let score: 10;

C. score let = 10;

D. let score = 10;

Solution

1. Step 1: Recall correct variable declaration syntax

   The correct syntax is: let variableName = value;

2. Step 2: Match syntax with options

   let score = 10; matches the correct syntax exactly.

3. Final Answer:

   let score = 10; -> Option D

4. Quick Check:

   Correct syntax = let score = 10; [OK]

Hint: Use: let variableName = value; [OK]

Common Mistakes:

• Placing let after variable name
• Using colon instead of equal sign
• Missing semicolon (though optional)

3. What will be the output of this code?

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

medium

A. 10

B. Error

C. undefined

D. 5

Solution

1. Step 1: Understand variable assignment and reassignment

   Variable x is first set to 5, then changed to 10.

2. Step 2: Check console.log output

   Since x was reassigned to 10, console.log(x) prints 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   Reassigned let variable prints new value [OK]

Hint: let variables can change value, so print latest [OK]

Common Mistakes:

• Thinking let variables cannot be reassigned
• Expecting original value to print
• Confusing with const behavior

4. Find the error in this code:

if (true) {
  let message = "Hello";
}
console.log(message);

medium

A. ReferenceError: message is not defined

B. SyntaxError: Unexpected token

C. No error, prints Hello

D. TypeError: message is undefined

Solution

1. Step 1: Understand block scope of let

   Variable message is declared inside the if block and only exists there.

2. Step 2: Check console.log outside block

   Trying to access message outside the block causes a ReferenceError.

3. Final Answer:

   ReferenceError: message is not defined -> Option A

4. Quick Check:

   let variables have block scope, so error outside block [OK]

Hint: let variables only exist inside their block [OK]

Common Mistakes:

• Assuming let variables are global
• Confusing ReferenceError with SyntaxError
• Trying to access block variables outside

5. Consider this code:

let total = 0;
for (let i = 0; i < 3; i++) {
  let total = i * 2;
}
console.log(total);

What will be printed and why?

hard

A. 6, because total sums all i*2 values

B. 4, because total accumulates inside the loop

C. 0, because the outer total is unchanged by inner block

D. ReferenceError, total is redeclared

Solution

1. Step 1: Identify variable scopes

   There are two total variables: one outside the loop and one declared inside the loop block.

2. Step 2: Understand variable shadowing

   The inner total inside the loop is a new variable that does not affect the outer total.

3. Step 3: Check final console.log

   The outer total remains 0, so console.log(total) prints 0.

4. Final Answer:

   0, because the outer total is unchanged by inner block -> Option C

5. Quick Check:

   Inner let shadows outer variable, outer stays 0 [OK]

Hint: Inner let creates new variable, outer stays same [OK]

Common Mistakes:

• Thinking inner total changes outer total
• Assuming let variables are global
• Confusing variable shadowing with reassignment