Global execution context in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of variable hoisting in global context

What is the output of the following JavaScript code when run in a browser console?

Javascript

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

A undefined\n10

B 10\n10

C ReferenceError: a is not defined

D undefined\nundefined

💡 Hint

Think about how variable declarations are hoisted but assignments are not.

In JavaScript, var declarations are hoisted to the top of their scope and initialized with undefined. So the first console.log(a) prints undefined. Then a is assigned 10, so the second console.log(a) prints 10.

❓ Predict Output

intermediate

Global object property from var declaration

What will be the output of this code snippet in a browser environment?

Javascript

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

A 5

B undefined

C ReferenceError

D null

💡 Hint

Consider how var variables relate to the global object in browsers.

In browsers, variables declared with var at the global scope become properties of the global window object. So window.x is 5.

❓ Predict Output

advanced

Output of let in global scope and window object

What will this code print in the browser console?

Javascript

let y = 20;
console.log(window.y);

A 20

B ReferenceError

C null

D undefined

💡 Hint

Think about how let differs from var in global scope.

Unlike var, let declarations at the global scope do NOT create properties on the global window object. So window.y is undefined.

❓ Predict Output

advanced

Global execution context and function declaration hoisting

What is the output of this code?

Javascript

foo();
function foo() {
  console.log('Hello from foo');
}
foo();

A TypeError: foo is not a function

B ReferenceError: foo is not defined

C Hello from foo\nHello from foo

D undefined\nHello from foo

💡 Hint

Remember how function declarations are hoisted completely.

Function declarations are hoisted with their body, so foo can be called before its definition. Both calls print 'Hello from foo'.

🧠 Conceptual

expert

Global execution context creation order

Which of the following correctly describes the order of steps when the JavaScript global execution context is created?

A Code execution phase, then variable and function declarations are hoisted

B Variable and function declarations are hoisted, then code execution phase runs

C Code execution phase runs, then global object is created

D Global object is created after code execution phase

💡 Hint

Think about what happens before the code runs.

When the global execution context is created, JavaScript first hoists all variable and function declarations (setting up memory space), then runs the code line by line.