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.