Why conditional logic is needed in Javascript - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this conditional code?

Look at this JavaScript code. What will it print to the console?

Javascript

const age = 20;
if (age >= 18) {
  console.log('Adult');
} else {
  console.log('Minor');
}

A "Adult"

B "Minor"

C undefined

D SyntaxError

💡 Hint

Check the condition if age is 18 or more.

Since age is 20, which is greater than or equal to 18, the code prints "Adult".

🧠 Conceptual

intermediate

Why do we use conditional logic in programs?

Choose the best reason why conditional logic is important in programming.

A To repeat the same code many times

B To make decisions and run different code based on conditions

C To store data permanently

D To make the program run faster

💡 Hint

Think about how a program chooses what to do next.

Conditional logic lets programs decide what to do based on different situations or inputs.

❓ Predict Output

advanced

What will this nested conditional code output?

Check the output of this JavaScript code with nested if-else statements.

Javascript

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

A "Grade A"

B ReferenceError

C "Grade C"

D "Grade B"

💡 Hint

Look at the score and check which condition it meets first.

Score 75 is not >= 90 but is >= 70, so it prints "Grade B".

🔧 Debug

advanced

Which option causes an error in this conditional code?

Find which code snippet will cause an error when run.

Javascript

const temperature = 30;
if temperature > 25 {
  console.log('Hot');
} else {
  console.log('Cold');
}

A if temperature > 25 { console.log('Hot'); } else { console.log('Cold'); }

B if (temperature > 25) { console.log('Hot'); } else { console.log('Cold'); }

C if (temperature > 25) console.log('Hot'); else console.log('Cold');

D temperature > 25 ? console.log('Hot') : console.log('Cold');

💡 Hint

Check the syntax of the if statement carefully.

Option A is missing parentheses around the condition, causing a SyntaxError.

🚀 Application

expert

What is the value of variable result after this code runs?

Consider this code using conditional logic and the ternary operator. What is the final value of result?

Javascript

const num = 10;
const result = num % 2 === 0 ? 'Even' : 'Odd';

A 10

B "Odd"

C "Even"

D undefined

💡 Hint

Check if 10 is divisible by 2 without remainder.

10 % 2 equals 0, so the condition is true and result is set to "Even".

Practice

1. Why do we use conditional logic like if and else in JavaScript?

easy

A. To make decisions and run different code based on conditions

B. To repeat the same code many times

C. To store multiple values in a list

D. To create new variables

Solution

1. Step 1: Understand the purpose of conditional logic

   Conditional logic allows the program to choose between different actions depending on conditions.

2. Step 2: Compare options with this purpose

   Only To make decisions and run different code based on conditions describes making decisions based on conditions, which matches the purpose of if and else.

3. Final Answer:

   To make decisions and run different code based on conditions -> Option A

4. Quick Check:

   Conditional logic = decision making [OK]

Hint: Think: Does it help choose between actions? [OK]

Common Mistakes:

• Confusing conditional logic with loops
• Thinking it stores data
• Believing it only creates variables

2. Which of the following is the correct syntax to check if a variable age is greater than 18 in JavaScript?

easy

A. if (age > 18) { }

B. if (age > 18) then { }

C. if age > 18 then { }

D. if age > 18 { }

Solution

1. Step 1: Recall JavaScript if statement syntax

   JavaScript requires parentheses around the condition and curly braces for the code block: if (condition) { }.

2. Step 2: Check each option

   if (age > 18) { } matches the correct syntax. Options A and C miss parentheses or use invalid keywords like 'then'. if (age > 18) then { } incorrectly uses 'then'.

3. Final Answer:

   if (age > 18) { } -> Option A

4. Quick Check:

   Correct if syntax = parentheses + braces [OK]

Hint: Remember: condition in ( ), code in { } [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using 'then' keyword (not in JavaScript)
• Missing curly braces

3. What will be the output of this code?

let score = 75;
if (score >= 60) {
  console.log('Pass');
} else {
  console.log('Fail');
}

medium

A. Fail

B. No output

C. Error

D. Pass

Solution

1. Step 1: Check the condition score >= 60

   The variable score is 75, which is greater than or equal to 60, so the condition is true.

2. Step 2: Determine which block runs

   Since the condition is true, the code inside the if block runs, printing 'Pass'.

3. Final Answer:

   Pass -> Option D

4. Quick Check:

   75 >= 60 is true, so output = Pass [OK]

Hint: Check if condition is true or false to pick output [OK]

Common Mistakes:

• Confusing which block runs on true condition
• Thinking output is 'Fail' for true condition
• Assuming syntax error

4. Find the error in this code snippet:

let temperature = 30;
if temperature > 25 {
  console.log('Hot');
} else {
  console.log('Cold');
}

medium

A. Using else without if

B. Missing semicolon after variable declaration

C. Missing parentheses around the condition in if statement

D. Incorrect variable name

Solution

1. Step 1: Check the if statement syntax

   JavaScript requires parentheses around the condition in an if statement, but here they are missing.

2. Step 2: Verify other parts

   The variable declaration is correct with semicolon, else is correctly used, and variable name matches.

3. Final Answer:

   Missing parentheses around the condition in if statement -> Option C

4. Quick Check:

   if needs (condition) [OK]

Hint: Always put condition inside ( ) after if [OK]

Common Mistakes:

• Forgetting parentheses in if condition
• Thinking semicolon is mandatory after if
• Confusing else usage

5. You want to write a program that prints 'Good morning' if the hour is less than 12, 'Good afternoon' if the hour is between 12 and 18 (inclusive), and 'Good evening' otherwise. Which code correctly uses conditional logic to do this?

hard

A. if (hour < 12) {
console.log('Good morning');
} else if (hour < 18) {
console.log('Good afternoon');
} else {
console.log('Good evening');
}

B. if (hour < 12) {
console.log('Good morning');
} else if (hour <= 18) {
console.log('Good afternoon');
} else {
console.log('Good evening');
}

C. if (hour <= 12) {
console.log('Good morning');
} else if (hour <= 18) {
console.log('Good afternoon');
} else {
console.log('Good evening');
}

D. if (hour < 12) {
console.log('Good morning');
} else if (hour > 12 && hour < 18) {
console.log('Good afternoon');
} else {
console.log('Good evening');
}

Solution

1. Step 1: Understand the conditions for each greeting

   'Good morning' if hour < 12, 'Good afternoon' if hour between 12 and 18 inclusive, else 'Good evening'.

2. Step 2: Check each option's condition ranges

   if (hour < 12) { console.log('Good morning'); } else if (hour <= 18) { console.log('Good afternoon'); } else { console.log('Good evening'); } correctly uses hour < 12 for morning, hour <= 18 for afternoon (including 12 and 18), else evening. Others miss inclusive 12 or 18 or have wrong ranges.

3. Final Answer:

   if (hour < 12) { console.log('Good morning'); } else if (hour <= 18) { console.log('Good afternoon'); } else { console.log('Good evening'); } -> Option B

4. Quick Check:

   Inclusive afternoon means <= 18, so if (hour < 12) { console.log('Good morning'); } else if (hour <= 18) { console.log('Good afternoon'); } else { console.log('Good evening'); } fits [OK]

Hint: Check if conditions cover all cases without gaps [OK]

Common Mistakes:

• Using < instead of <= for inclusive ranges
• Overlapping or missing ranges
• Wrong logical operators in conditions