Global scope in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code involving global and local variables?

Consider the following JavaScript code:

var x = 10;
function test() {
  var x = 20;
  console.log(x);
}
test();
console.log(x);

What will be printed to the console?

Javascript

var x = 10;
function test() {
  var x = 20;
  console.log(x);
}
test();
console.log(x);

A 20\n10

B 10\n20

C 20\n20

D 10\n10

💡 Hint

Remember that variables declared inside a function have local scope and do not affect the global variable.

The function test has a local variable x set to 20, so console.log(x) inside the function prints 20. Outside the function, the global x is still 10, so console.log(x) prints 10.

❓ Predict Output

intermediate

What happens when you omit var/let/const in a function?

Look at this code:

function setValue() {
  y = 5;
}
setValue();
console.log(y);

What will be the output?

Javascript

function setValue() {
  y = 5;
}
setValue();
console.log(y);

A TypeError

B ReferenceError: y is not defined

C undefined

D 5

💡 Hint

Variables assigned without var, let, or const inside functions become global.

Because y is assigned without declaration inside the function, it becomes a global variable. So after calling setValue(), y exists globally with value 5.

🧠 Conceptual

advanced

Which statement about global scope is true?

Choose the correct statement about global scope in JavaScript.

A Variables declared with <code>let</code> at the top level become properties of the global object.

B Variables declared with <code>var</code> at the top level become properties of the global object.

C Using <code>const</code> inside a function creates a global variable.

D Functions declared inside blocks are always global.

💡 Hint

Think about how var and let differ in global scope.

Variables declared with var at the top level become properties of the global object (like window in browsers). Variables declared with let or const do not become global object properties. Functions declared inside blocks are block-scoped, not global. const inside functions is local to that function.

❓ Predict Output

advanced

What is the output when modifying a global variable inside a function?

Consider this code:

let count = 0;
function increment() {
  count++;
}
increment();
console.log(count);

What will be printed?

Javascript

let count = 0;
function increment() {
  count++;
}
increment();
console.log(count);

A ReferenceError

B NaN

C 1

D 0

💡 Hint

Variables declared with let at global scope can be accessed and changed inside functions.

The variable count is declared globally with let. The function increment increases it by 1. So after calling increment(), count becomes 1.

❓ Predict Output

expert

What is the output of this code with nested scopes and global variable?

Analyze this code snippet:

var a = 1;
function outer() {
  var a = 2;
  function inner() {
    a = 3;
  }
  inner();
  console.log(a);
}
outer();
console.log(a);

What will be printed to the console?

Javascript

var a = 1;
function outer() {
  var a = 2;
  function inner() {
    a = 3;
  }
  inner();
  console.log(a);
}
outer();
console.log(a);

A 3\n1

B 3\n3

C 2\n3

D 2\n1

💡 Hint

Remember that inner changes the a in outer's scope, not the global a.

The variable a inside outer is initially 2. The inner function changes this a to 3. So console.log(a) inside outer prints 3. The global a remains 1, so the last console.log(a) prints 1.