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

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of var variable hoisting

What is the output of this JavaScript code?

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

Javascript

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

A undefined\n5

B undefined\nundefined

C 5\n5

D ReferenceError: x is not defined

💡 Hint

Think about how var variables are hoisted but not initialized.

Variables declared with var are hoisted to the top of their scope but initialized with undefined until the assignment line runs. So the first console.log prints undefined, the second prints 5.

❓ Predict Output

intermediate

var variable scope inside function

What will be the output of this code?

function test() {
  var a = 10;
  if (true) {
    var a = 20;
    console.log(a);
  }
  console.log(a);
}
test();

Javascript

function test() {
  var a = 10;
  if (true) {
    var a = 20;
    console.log(a);
  }
  console.log(a);
}
test();

A 10\n20

B 20\n20

C 20\n10

D ReferenceError

💡 Hint

Remember var is function scoped, not block scoped.

The var declaration inside the if block overwrites the function scoped variable a. So both console.logs print 20.

❓ Predict Output

advanced

var redeclaration behavior

What is the output of this code?

var x = 1;
var x = 2;
console.log(x);

Javascript

var x = 1;
var x = 2;
console.log(x);

A SyntaxError

B 1

C 2

D ReferenceError

💡 Hint

var allows redeclaration without error.

Redeclaring a var variable simply overwrites the previous value. So x becomes 2.

❓ Predict Output

advanced

var variable in loops and closures

What will this code print?

var funcs = [];
for (var i = 0; i < 3; i++) {
  funcs.push(function() { return i; });
}
console.log(funcs[0]());
console.log(funcs[1]());
console.log(funcs[2]());

Javascript

var funcs = [];
for (var i = 0; i < 3; i++) {
  funcs.push(function() { return i; });
}
console.log(funcs[0]());
console.log(funcs[1]());
console.log(funcs[2]());

A ReferenceError

B 0\n1\n2

C undefined\nundefined\nundefined

D 3\n3\n3

💡 Hint

var is function scoped, so all functions share the same i.

The variable i is shared in the loop and after the loop ends i is 3. All functions return 3.

🧠 Conceptual

expert

var variable redeclaration and hoisting combined

Consider this code snippet:

console.log(a);
var a = 10;
var a = 20;
console.log(a);

What will be the output when this code runs?

Javascript

console.log(a);
var a = 10;
var a = 20;
console.log(a);

A undefined\n20

B 10\n20

C ReferenceError\n20

D undefined\n10

💡 Hint

var declarations are hoisted and redeclarations overwrite previous values.

The first console.log prints undefined because a is hoisted but not initialized yet. The redeclaration does not cause error and the last assignment sets a to 20, so second console.log prints 20.

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