JavaScript execution flow - Mini Project: Build & Apply

Understanding JavaScript Execution Flow

📖 Scenario: Imagine you are baking a cake. You have a list of steps to follow in order. In JavaScript, the computer also follows steps one by one. This project will help you see how JavaScript runs code from top to bottom.

🎯 Goal: You will write a simple JavaScript program with variables and functions to see how the code runs step by step. You will learn how JavaScript executes commands in order and how functions are called.

📋 What You'll Learn

Create variables with exact names and values

Create a function with a specific name

Call the function in the right place

Print output using console.log exactly as instructed

💡 Why This Matters

🌍 Real World

Understanding execution flow helps you write programs that do tasks in the right order, like following a recipe.

💼 Career

Every programmer needs to know how code runs step by step to debug and build working applications.

1

Create variables for ingredients

Create two variables called flour and sugar. Set flour to 2 and sugar to 1.

Javascript

// Create variables flour and sugar with values 2 and 1
// Your code here

Hint

Use let to create variables and assign the numbers 2 and 1.

2

Create a function to mix ingredients

Create a function called mixIngredients that returns the sum of flour and sugar.

Javascript

let flour = 2;
let sugar = 1;

// Create function mixIngredients that returns flour + sugar
// Your code here

Hint

Define a function using the function keyword and return the sum of the two variables.

3

Call the function and store the result

Create a variable called batter and set it to the result of calling the function mixIngredients().

Javascript

let flour = 2;
let sugar = 1;

function mixIngredients() {
    return flour + sugar;
}

// Call mixIngredients and store result in batter
// Your code here

Hint

Call the function by writing its name followed by parentheses and assign the result to batter.

4

Print the batter amount

Use console.log to print the value of the variable batter.

Javascript

let flour = 2;
let sugar = 1;

function mixIngredients() {
    return flour + sugar;
}

let batter = mixIngredients();

// Print batter using console.log
// Your code here

Hint

Use console.log(batter); to show the value in the console.

Practice

1. What happens when JavaScript encounters a function declaration in the code?

easy

A. The function runs immediately.

B. The function is stored but not run until called.

C. The function is ignored.

D. The function causes an error.

Solution

1. Step 1: Understand function declaration behavior

   When JavaScript sees a function declared, it saves it in memory but does not execute it immediately.

2. Step 2: Recognize when functions run

   Functions only run when they are explicitly called later in the code.

3. Final Answer:

   The function is stored but not run until called. -> Option B

4. Quick Check:

   Functions run only when called = A [OK]

Hint: Functions run only when called, not on declaration [OK]

Common Mistakes:

• Thinking functions run immediately on declaration
• Confusing declaration with invocation
• Assuming functions are ignored until called

2. Which of the following is the correct way to call a function named greet in JavaScript?

easy

A. greet();

B. greet;

C. call greet();

D. function greet();

Solution

1. Step 1: Identify function call syntax

   In JavaScript, calling a function requires the function name followed by parentheses.

2. Step 2: Check each option

   greet(); uses greet(); which correctly calls the function. Others are incorrect syntax.

3. Final Answer:

   greet(); -> Option A

4. Quick Check:

   Function call needs parentheses = A [OK]

Hint: Call functions with parentheses: name() [OK]

Common Mistakes:

• Forgetting parentheses when calling functions
• Using 'call' keyword incorrectly
• Confusing declaration syntax with call

3. What will be the output of the following code?

console.log('Start');
setTimeout(() => console.log('Timeout'), 0);
console.log('End');

medium

A. StartEndTimeout

B. EndStartTimeout

C. TimeoutStartEnd

D. StartTimeoutEnd

Solution

1. Step 1: Understand synchronous and asynchronous code

   console.log('Start') runs first and prints 'Start'. setTimeout schedules a function to run later, after current code finishes.

2. Step 2: Trace the execution order

   console.log('End') runs immediately after 'Start'. Then the setTimeout callback runs, printing 'Timeout'.

3. Final Answer:

   Start
   End
   Timeout -> Option A

4. Quick Check:

   Async runs after sync code = D [OK]

Hint: setTimeout runs after current code finishes [OK]

Common Mistakes:

• Assuming setTimeout runs immediately
• Mixing order of console logs
• Ignoring asynchronous behavior

4. Find the error in this code snippet:

function sayHi() {
  console.log('Hi');
}
sayHi

medium

A. console.log syntax error

B. Function name is incorrect

C. Missing parentheses to call the function

D. No error, code runs fine

Solution

1. Step 1: Check function call syntax

   The code writes sayHi without parentheses, so the function is not called.

2. Step 2: Identify the fix

   Adding parentheses sayHi() calls the function and prints 'Hi'.

3. Final Answer:

   Missing parentheses to call the function -> Option C

4. Quick Check:

   Function call needs () = C [OK]

Hint: Always use () to call functions [OK]

Common Mistakes:

• Forgetting parentheses to invoke functions
• Thinking function name alone calls it
• Assuming no error when function not called

5. Consider this code:

console.log('1');
setTimeout(() => console.log('2'), 100);
Promise.resolve().then(() => console.log('3'));
console.log('4');

What is the correct order of output?

hard

A. 1342

B. 4132

C. 1234

D. 1432

Solution

1. Step 1: Understand synchronous, microtask, and macrotask queues

   console.log('1') and console.log('4') run immediately (sync). Promise.then callbacks run next (microtask). setTimeout callbacks run last (macrotask).

2. Step 2: Trace output order

   Output order is '1' (sync), '4' (sync), '3' (Promise microtask), then '2' (setTimeout macrotask).

3. Final Answer:

   1
   4
   3
   2 -> Option D

4. Quick Check:

   Promise microtasks before setTimeout macrotasks = B [OK]

Hint: Promise.then runs before setTimeout even with 0 delay [OK]

Common Mistakes:

• Thinking setTimeout runs before Promise.then
• Ignoring microtask queue priority
• Assuming all async run in order scheduled