Variable declaration using var in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Javascript

var [1] = 25;

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

Anumber

Blet

Cconst

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using keywords like let or const instead of the variable name.

Using a number or type instead of a variable name.

Use var followed by the variable name age to declare it.

2fill in blank

medium

Complete the code to declare a variable named name and assign it the value 'Alice' using var.

Javascript

var [1] = 'Alice';

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

Alet

Bconst

Cname

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using let or const instead of the variable name.

Using a type name like string instead of the variable name.

The variable name should be name to store the string 'Alice'.

3fill in blank

hard

Fix the error in the code by completing the variable declaration with var.

Javascript

[1] score = 100;

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

Avar

Blet

Cconst

Dscore

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the keyword var.

Using let or const instead of var.

The keyword var is needed to declare the variable score.

4fill in blank

hard

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

Javascript

var [1] = 5, [2] = 10;

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

Ax

Bvar

Cy

Dlet

Attempts:

3 left

💡 Hint

Common Mistakes

Using let instead of var.

Using the keyword var twice.

Using wrong variable names.

Use variable names x and y after the var keyword to declare both variables.

5fill in blank

hard

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

Javascript

var [1] = 1, [2] = 2, [3] = 3;

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

Aa

Bb

Cc

Dlet

Attempts:

3 left

💡 Hint

Common Mistakes

Using let instead of var.

Using wrong variable names or order.

Missing commas between variables.

Declare variables a, b, and c separated by commas after the var keyword.

Practice

1. What does the var keyword do in JavaScript?

easy

A. Declares a block-scoped variable

B. Declares a constant that cannot be changed

C. Declares a variable that can be changed and redeclared

D. Declares a variable only inside loops

Solution

1. Step 1: Understand var behavior

   var declares variables that can be changed and redeclared in the same scope.

2. Step 2: Compare with other declarations

   Unlike const or let, var is function-scoped and allows redeclaration.

3. Final Answer:

   Declares a variable that can be changed and redeclared -> Option C

4. Quick Check:

   var allows redeclaration = A [OK]

Hint: Remember: var variables can be changed and redeclared easily [OK]

Common Mistakes:

• Confusing var with const or let
• Thinking var is block-scoped
• Assuming var variables cannot be redeclared

2. Which of the following is the correct syntax to declare a variable using var?

easy

A. var myVar = 10;

B. variable myVar = 10;

C. var: myVar = 10;

D. v ar myVar = 10;

Solution

1. Step 1: Recall correct var syntax

   The correct syntax is var variableName = value; with no spaces or colons.

2. Step 2: Check each option

   Only var myVar = 10; matches the correct syntax exactly.

3. Final Answer:

   var myVar = 10; -> Option A

4. Quick Check:

   Correct var syntax = A [OK]

Hint: Use 'var name = value;' format without extra symbols [OK]

Common Mistakes:

• Using 'variable' instead of 'var'
• Adding colons after var
• Adding spaces inside 'var'

3. What will be the output of this code?

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

medium

A. 5

B. Error

C. undefined

D. 10

Solution

1. Step 1: Understand redeclaration with var

   Using var, redeclaring a variable overwrites its previous value.

2. Step 2: Trace the code execution

   First x is 5, then redeclared as 10, so console.log(x) prints 10.

3. Final Answer:

   10 -> Option D

4. Quick Check:

   Redeclared var overwrites value = 10 [OK]

Hint: Redeclaring var overwrites previous value [OK]

Common Mistakes:

• Thinking redeclaration causes error
• Expecting first value to print
• Confusing var with let or const behavior

4. Find the error in this code snippet:

if (true) {
  var a = 1;
}
console.log(a);

medium

A. ReferenceError: a is not defined

B. No error, prints 1

C. TypeError: a is not a function

D. SyntaxError due to missing braces

Solution

1. Step 1: Understand var scope

   var is function-scoped, not block-scoped, so a is accessible outside the if block.

2. Step 2: Check console.log output

   Since a is declared with var, console.log(a) prints 1 without error.

3. Final Answer:

   No error, prints 1 -> Option B

4. Quick Check:

   var is function-scoped, so prints 1 [OK]

Hint: var ignores block scope, accessible outside blocks [OK]

Common Mistakes:

• Assuming var is block-scoped like let
• Expecting ReferenceError outside block
• Confusing var with const or let scope

5. Consider this code:

function test() {
  if (true) {
    var count = 5;
  }
  var count = 10;
  return count;
}
console.log(test());

What will be the output and why?

hard

A. 10 because second var redeclares and overwrites

B. Error due to redeclaration of count

C. 5 because first var inside if is used

D. undefined because var is block-scoped

Solution

1. Step 1: Analyze var declarations inside function

   Both var count declarations are in the same function scope, so the second redeclaration overwrites the first.

2. Step 2: Determine returned value

   The function returns the last assigned value, which is 10.

3. Final Answer:

   10 because second var redeclares and overwrites -> Option A

4. Quick Check:

   Function-scoped var redeclaration overwrites = 10 [OK]

Hint: Inside functions, var redeclaration overwrites previous value [OK]

Common Mistakes:

• Thinking redeclaration causes error
• Assuming block scope limits var
• Expecting first value to be returned