What execution context is in Javascript - Mini Project: Build & Apply

What execution context is

📖 Scenario: Imagine you are baking cookies in a kitchen. The kitchen is your workspace where you have all your ingredients and tools ready. In programming, the execution context is like that kitchen where your code runs and has access to everything it needs.

🎯 Goal: You will create a simple JavaScript program that shows how the execution context works by running code inside a function and logging messages to understand where the code is running.

📋 What You'll Learn

Create a variable in the global context

Create a function to represent a new execution context

Use console.log to show messages from global and function contexts

Call the function to see the execution context in action

💡 Why This Matters

🌍 Real World

Understanding execution context helps you know where your variables live and how your code runs step-by-step, which is important for debugging and writing clear code.

💼 Career

Many programming jobs require you to understand how code runs in different contexts to avoid bugs and write efficient, maintainable code.

1

Create a global variable

Create a variable called message in the global context and set it to the string 'Hello from global context'.

Javascript

// Create a variable called message in the global context
// Your code here

Hint

Use var to create a variable named message and assign the exact string.

2

Create a function to represent a new execution context

Create a function called showContext that creates a variable called message inside it with the value 'Hello from function context'.

Javascript

var message = 'Hello from global context';
// Create a function called showContext with a variable message inside
// Your code here

Hint

Define a function named showContext and inside it, create a variable message with the exact string.

3

Log messages from both contexts

Inside the showContext function, add two console.log statements: one to print the local message variable, and one to print the global message variable using window.message.

Javascript

var message = 'Hello from global context';
function showContext() {
    const message = 'Hello from function context';
    // Add console.log to print local message
    // Add console.log to print global message using window.message
    // Your code here
}

Hint

Use console.log(message) to print the local message and console.log(window.message) to print the global message.

4

Call the function and see the output

Call the function showContext() to run the code and see the messages from both execution contexts printed in the console.

Javascript

var message = 'Hello from global context';
function showContext() {
    const message = 'Hello from function context';
    console.log(message);
    console.log(window.message);
}
// Call the showContext function
// Your code here

Hint

Simply call showContext() to run the function and see the output.

Practice

1. What is an execution context in JavaScript?

easy

A. The environment where JavaScript code runs and variables/functions are accessible

B. A special type of variable that stores data temporarily

C. A function that executes automatically when the page loads

D. A tool used to debug JavaScript code in the browser

Solution

1. Step 1: Understand the meaning of execution context

   Execution context is the environment where JavaScript code runs, controlling variable and function access.

2. Step 2: Compare options with the definition

   Only The environment where JavaScript code runs and variables/functions are accessible correctly describes this environment; others describe unrelated concepts.

3. Final Answer:

   The environment where JavaScript code runs and variables/functions are accessible -> Option A

4. Quick Check:

   Execution context = environment for code execution [OK]

Hint: Execution context = where code runs and variables live [OK]

Common Mistakes:

• Confusing execution context with variables
• Thinking it's a debugging tool
• Mixing it up with functions

2. Which of the following is a valid type of execution context in JavaScript?

easy

A. Global, Function, and Block execution contexts

B. Local, Remote, and Server execution contexts

C. Compile-time, Run-time, and Debug execution contexts

D. Synchronous, Asynchronous, and Parallel execution contexts

Solution

1. Step 1: Recall the types of execution contexts

   JavaScript has three main execution contexts: Global, Function, and Block.

2. Step 2: Match options with known types

   Only Global, Function, and Block execution contexts lists the correct types; others list unrelated or incorrect terms.

3. Final Answer:

   Global, Function, and Block execution contexts -> Option A

4. Quick Check:

   Execution context types = Global, Function, Block [OK]

Hint: Remember the three main contexts: Global, Function, Block [OK]

Common Mistakes:

• Confusing execution context types with networking terms
• Mixing compile/run-time concepts
• Thinking async types are execution contexts

3. Consider the code:

let x = 10;
function foo() {
  let y = 20;
  console.log(x + y);
}
foo();

Which execution context is active when console.log runs?

medium

A. Global execution context only

B. Function execution context of foo

C. Block execution context inside foo

D. No execution context is active

Solution

1. Step 1: Identify where console.log is called

   It is inside the function foo, so the function's execution context is active.

2. Step 2: Understand execution context hierarchy

   When foo runs, its function execution context is created and active during console.log.

3. Final Answer:

   Function execution context of foo -> Option B

4. Quick Check:

   Inside function = function execution context active [OK]

Hint: Code inside function runs in function execution context [OK]

Common Mistakes:

• Thinking only global context is active
• Confusing block context with function context
• Believing no context is active during execution

4. Find the error in this code related to execution context:

function test() {
  console.log(a);
  let a = 5;
}
test();

medium

A. SyntaxError due to missing semicolon

B. No error, outputs 5

C. ReferenceError because a is used before declaration

D. TypeError because a is not a function

Solution

1. Step 1: Analyze variable declaration and usage

   a is declared with let after it is logged, so it is in the temporal dead zone.

2. Step 2: Understand execution context and hoisting

   let variables are not hoisted like var, causing a ReferenceError when accessed before declaration.

3. Final Answer:

   ReferenceError because a is used before declaration -> Option C

4. Quick Check:

   Accessing let before declaration = ReferenceError [OK]

Hint: Accessing let/const before declaration causes ReferenceError [OK]

Common Mistakes:

• Thinking it outputs undefined
• Confusing with var hoisting
• Ignoring temporal dead zone

5. You want to create a block execution context to limit variable scope inside an if statement. Which code correctly creates a block execution context?

hard

A. let x = 10;
console.log(x);

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

C. if (true)
var x = 10;
console.log(x);

D. if (true) {
let x = 10;
console.log(x);
}

Solution

1. Step 1: Identify block execution context creation

   Block execution context is created by blocks like { ... } with let or const variables.

2. Step 2: Check each option for block scope

   if (true) {
     let x = 10;
     console.log(x);
   }

   uses let inside an if block, creating a block execution context. Others use function or global scope.

3. Final Answer:

   if (true) { let x = 10; console.log(x); } -> Option D

4. Quick Check:

   Block scope needs { } and let/const [OK]

Hint: Use { } with let/const to create block execution context [OK]

Common Mistakes:

• Using var inside if block expecting block scope
• Not using braces for block
• Confusing function scope with block scope