Why loops are needed in Javascript - See It in Action

Why loops are needed

📖 Scenario: Imagine you have a list of fruits and you want to say hello to each fruit one by one. Doing this without loops means writing the same message many times. Loops help us repeat actions easily.

🎯 Goal: You will create a list of fruits, set up a counter, use a loop to greet each fruit, and finally print all greetings.

📋 What You'll Learn

Create an array called fruits with these exact values: "Apple", "Banana", "Cherry"

Create a variable called greetings and set it to an empty array

Use a for loop with variable i to go through fruits

Inside the loop, add a greeting string `Hello, ${fruits[i]}!` to greetings

Print the greetings array

💡 Why This Matters

🌍 Real World

Loops are used in many apps to process lists of items, like showing messages for each user or calculating totals.

💼 Career

Understanding loops is essential for any programming job because they make code efficient and easier to maintain.

1

Create the fruits array

Create an array called fruits with these exact values: "Apple", "Banana", "Cherry"

Javascript

# Create the fruits array
// Your code here

Hint

Use square brackets [] to create an array and separate items with commas.

2

Create an empty greetings array

Create a variable called greetings and set it to an empty array []

Javascript

const fruits = ["Apple", "Banana", "Cherry"];
// Create an empty greetings array
// Your code here

Hint

An empty array is created with [].

3

Use a for loop to add greetings

Use a for loop with variable i to go through fruits. Inside the loop, add a greeting string `Hello, ${fruits[i]}!` to the greetings array using push()

Javascript

const fruits = ["Apple", "Banana", "Cherry"];
const greetings = [];
// Use a for loop to add greetings
// Your code here

Hint

Use fruits.length to get the number of fruits and push() to add items to the array.

4

Print the greetings array

Write console.log(greetings) to print the greetings array

Javascript

const fruits = ["Apple", "Banana", "Cherry"];
const greetings = [];
for (let i = 0; i < fruits.length; i++) {
    greetings.push(`Hello, ${fruits[i]}!`);
}
// Print the greetings array
// Your code here

Hint

Use console.log() to show the array in the console.

Practice

1. Why do we use loops in JavaScript?
for or while loops help us to:

easy

A. Repeat a task multiple times without writing it again

B. Write code only once and never run it

C. Make the program run slower

D. Stop the program from running

Solution

1. Step 1: Understand the purpose of loops

   Loops allow repeating the same action many times without rewriting the code.

2. Step 2: Compare options with loop purpose

   Only Repeat a task multiple times without writing it again matches this purpose by saying loops repeat tasks multiple times.

3. Final Answer:

   Repeat a task multiple times without writing it again -> Option A

4. Quick Check:

   Loops repeat tasks = B [OK]

Hint: Loops repeat code to save writing it many times [OK]

Common Mistakes:

• Thinking loops slow down the program
• Believing loops stop the program
• Confusing loops with one-time code

2. Which of these is the correct syntax to start a for loop in JavaScript?

easy

A. for (let i = 0; i < 5; i++) { }

B. for i in range(5) { }

C. loop (i = 0; i < 5; i++) { }

D. for i = 0 to 5 { }

Solution

1. Step 1: Recall JavaScript for loop syntax

   The correct syntax uses parentheses with initialization, condition, and increment separated by semicolons.

2. Step 2: Match options to syntax

   for (let i = 0; i < 5; i++) { } matches this exactly: for (let i = 0; i < 5; i++) { }.

3. Final Answer:

   for (let i = 0; i < 5; i++) { } -> Option A

4. Quick Check:

   JS for loop syntax = D [OK]

Hint: JS for loops use semicolons inside parentheses [OK]

Common Mistakes:

• Using Python or other language syntax
• Missing parentheses or semicolons
• Using wrong keywords like 'loop'

3. What will this code print?

for (let i = 1; i <= 3; i++) {
  console.log(i);
}

medium

A. 0 1 2

B. 1 2 3

C. 1 2 3 4

D. 3 2 1

Solution

1. Step 1: Analyze loop start and end values

   The loop starts at i=1 and runs while i is less than or equal to 3.

2. Step 2: List printed values

   It prints 1, then 2, then 3, then stops because i becomes 4.

3. Final Answer:

   1 2 3 -> Option B

4. Quick Check:

   Loop prints 1 to 3 = C [OK]

Hint: Check loop start, end, and condition carefully [OK]

Common Mistakes:

• Starting count from 0 instead of 1
• Including number 4 by mistake
• Printing in reverse order

4. Find the error in this loop:

for (let i = 0; i < 5; i++)
  console.log(i)
}

medium

A. Missing opening brace { after for statement

B. Incorrect loop condition

C. Variable i is not declared

D. Extra closing brace } without matching {

Solution

1. Step 1: Check braces in the code

   The loop has no opening brace { but has a closing brace } at the end.

2. Step 2: Identify mismatch

   Extra closing brace } without a matching opening brace causes syntax error.

3. Final Answer:

   Extra closing brace } without matching { -> Option D

4. Quick Check:

   Brace mismatch error = A [OK]

Hint: Count opening and closing braces carefully [OK]

Common Mistakes:

• Forgetting to add opening brace {
• Assuming missing semicolon causes error here
• Not noticing extra closing brace

5. You want to print all even numbers from 2 to 10 using a loop. Which code correctly does this?

hard

A. for (let i = 2; i < 10; i++) { console.log(i); }

B. for (let i = 0; i <= 10; i++) { if (i % 2 === 0) console.log(i); }

C. for (let i = 2; i <= 10; i += 2) { console.log(i); }

D. for (let i = 0; i <= 10; i += 3) { console.log(i); }

Solution

1. Step 1: Understand the goal

   We want to print even numbers from 2 to 10 inclusive.

2. Step 2: Check each option

   for (let i = 2; i <= 10; i += 2) { console.log(i); } starts at 2, increments by 2, and stops at 10, printing 2,4,6,8,10 correctly.

3. Final Answer:

   for (let i = 2; i <= 10; i += 2) { console.log(i); } -> Option C

4. Quick Check:

   Increment by 2 from 2 to 10 = A [OK]

Hint: Use step of 2 to print even numbers directly [OK]

Common Mistakes:

• Printing odd numbers by mistake
• Stopping before 10
• Using wrong increment step