Else–if ladder in Javascript - Mini Project: Build & Apply

Else-if ladder

📖 Scenario: You are creating a simple program that gives a message based on the temperature outside. This helps people decide what to wear.

🎯 Goal: Build a program that uses an else if ladder to check the temperature and print the right message.

📋 What You'll Learn

Create a variable called temperature with a number value.

Create a variable called message to store the result message.

Use an else if ladder to set message based on temperature:

temperature >= 30 -> message is "It's very hot outside."

temperature >= 20 -> message is "The weather is warm."

temperature >= 10 -> message is "It's a bit chilly."

Otherwise, message is "It's cold outside."

Print the message.

💡 Why This Matters

🌍 Real World

Checking temperature and giving advice is common in weather apps and smart home devices.

💼 Career

Understanding conditional logic like else if ladders is essential for programming decisions in many software projects.

1

Create the temperature variable

Create a variable called temperature and set it to the number 25.

Javascript

// Your code here

Hint

Use let temperature = 25; to create the variable.

2

Create the message variable

Create a variable called message and set it to an empty string "".

Javascript

let temperature = 25;
// Your code here

Hint

Use let message = ""; to create the variable.

3

Use else if ladder to set the message

Use an if statement with an else if ladder to set message based on temperature as follows:
- If temperature >= 30, set message = "It's very hot outside."
- Else if temperature >= 20, set message = "The weather is warm."
- Else if temperature >= 10, set message = "It's a bit chilly."
- Else, set message = "It's cold outside."

Javascript

let temperature = 25;
let message = "";
// Your code here

Hint

Use if, else if, and else to check the temperature ranges and set the message.

4

Print the message

Write console.log(message); to print the message to the console.

Javascript

let temperature = 25;
let message = "";

if (temperature >= 30) {
    message = "It's very hot outside.";
} else if (temperature >= 20) {
    message = "The weather is warm.";
} else if (temperature >= 10) {
    message = "It's a bit chilly.";
} else {
    message = "It's cold outside.";
}
// Your code here

Hint

Use console.log(message); to show the message.

Practice

1. What does an else if ladder do in JavaScript?

easy

A. Only runs the last condition regardless of others

B. Runs all true conditions in sequence

C. Checks multiple conditions one by one and runs the first true block

D. Skips all conditions and runs default code

Solution

1. Step 1: Understand else if ladder behavior

   An else if ladder checks conditions in order, one after another.

2. Step 2: Identify which block runs

   Only the first condition that is true will run its code block; others are skipped.

3. Final Answer:

   Checks multiple conditions one by one and runs the first true block -> Option C

4. Quick Check:

   else if ladder = first true block runs [OK]

Hint: Remember: else if stops at first true condition [OK]

Common Mistakes:

• Thinking all true blocks run
• Confusing else if with separate if statements
• Believing else if runs last condition only

2. Which of the following is the correct syntax for an else if ladder in JavaScript?

easy

A. if (x > 10) {} else if (x > 5) {} else {}

B. if x > 10 then {} else if x > 5 then {} else {}

C. if (x > 10) {} elseif (x > 5) {} else {}

D. if (x > 10) {} else (x > 5) {} else {}

Solution

1. Step 1: Check JavaScript syntax rules

   JavaScript uses parentheses around conditions and keywords: if, else if, else.

2. Step 2: Identify correct else if syntax

   The correct keyword is else if with a space, not elseif or missing parentheses.

3. Final Answer:

   if (x > 10) {} else if (x > 5) {} else {} -> Option A

4. Quick Check:

   Correct else if syntax = if (x > 10) {} else if (x > 5) {} else {} [OK]

Hint: Use 'else if' with space and parentheses [OK]

Common Mistakes:

• Writing 'elseif' as one word
• Omitting parentheses around conditions
• Using else with a condition directly

3. What will be the output of this code?

let score = 75;
if (score >= 90) {
  console.log('A');
} else if (score >= 80) {
  console.log('B');
} else if (score >= 70) {
  console.log('C');
} else {
  console.log('F');
}

medium

A. A

B. C

C. B

D. F

Solution

1. Step 1: Check conditions in order

   score is 75, so first condition (>=90) is false, second (>=80) is false, third (>=70) is true.

2. Step 2: Identify which block runs

   The third else if block runs and prints 'C'. The else block is skipped.

3. Final Answer:

   C -> Option B

4. Quick Check:

   First true condition output = C [OK]

Hint: Check conditions top to bottom, first true runs [OK]

Common Mistakes:

• Picking output 'B' or 'A' incorrectly
• Ignoring order of conditions
• Assuming else runs when a condition is true

4. Find the error in this else if ladder code:

let num = 10;
if (num > 10) {
  console.log('Greater than 10');
} else if num > 5 {
  console.log('Greater than 5');
} else {
  console.log('5 or less');
}

medium

A. No error, code is correct

B. Missing curly braces in if block

C. Using else if instead of else

D. Missing parentheses around condition in else if

Solution

1. Step 1: Check syntax of else if condition

   In JavaScript, conditions must be inside parentheses, but here else if condition lacks parentheses.

2. Step 2: Confirm other parts are correct

   Curly braces are present, and else if is correctly used, so no other syntax errors.

3. Final Answer:

   Missing parentheses around condition in else if -> Option D

4. Quick Check:

   Conditions need parentheses [OK]

Hint: Always put conditions inside parentheses [OK]

Common Mistakes:

• Forgetting parentheses in else if
• Confusing else if with else
• Missing curly braces

5. You want to assign a grade based on score using else if ladder. Which code correctly assigns 'Pass' if score is 50 or more, 'Fail' if less, and 'Invalid' if score is negative?

let score = 45;
if (score < 0) {
  console.log('Invalid');
} else if (score >= 50) {
  console.log('Pass');
} else {
  console.log('Fail');
}

hard

A. Correctly assigns grades as per conditions

B. Fails to check negative score first

C. Pass and Fail conditions are swapped

D. Missing else if for negative score

Solution

1. Step 1: Check order of conditions

   Negative score is checked first, so invalid scores are caught early.

2. Step 2: Verify pass and fail conditions

   Score >= 50 prints 'Pass', else prints 'Fail'. This matches requirements.

3. Final Answer:

   Correctly assigns grades as per conditions -> Option A

4. Quick Check:

   Order and conditions correct = Correctly assigns grades as per conditions [OK]

Hint: Check invalid cases first in else if ladder [OK]

Common Mistakes:

• Checking pass before invalid score
• Swapping pass and fail conditions
• Missing else block for fail