Why conditional logic is needed in Javascript - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a number is positive.

Javascript

if (number [1] 0) {
  console.log('Positive number');
}

Drag options to blanks, or click blank then click option'

A!=

B<

C===

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' checks for negative numbers, not positive.

Using '===' checks for equality, not greater than.

We use the greater than symbol > to check if the number is more than zero, meaning positive.

2fill in blank

medium

Complete the code to print 'Even' if the number is divisible by 2.

Javascript

if (number [1] 2 === 0) {
  console.log('Even');
}

Drag options to blanks, or click blank then click option'

A-

B%

C+

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' or '-' will not check divisibility.

Using '*' multiplies, not divides.

The modulus operator % gives the remainder. If remainder is 0 when divided by 2, the number is even.

3fill in blank

hard

Fix the error in the condition to check if age is 18 or older.

Javascript

if (age [1] 18) {
  console.log('Adult');
}

Drag options to blanks, or click blank then click option'

A>=

B==

C<=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '<=' checks for younger ages.

Using '==' checks only for exactly 18.

We use >= to check if age is 18 or more, meaning adult.

4fill in blank

hard

Fill both blanks to check if a number is between 10 and 20 (inclusive).

Javascript

if (number [1] 10 && number [2] 20) {
  console.log('Between 10 and 20');
}

Drag options to blanks, or click blank then click option'

A>=

B<

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' for the first blank would exclude 10.

Using '>' for the second blank would exclude 20.

Use >= to check number is at least 10, and <= to check number is at most 20.

5fill in blank

hard

Fill all three blanks to create an if-else that prints 'Child', 'Teen', or 'Adult' based on age.

Javascript

if (age [1] 12) {
  console.log('Child');
} else if (age [2] 19) {
  console.log([3]);
} else {
  console.log('Adult');
}

Drag options to blanks, or click blank then click option'

A<=

B<

C'Adult'

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>=' in first blank reverses logic.

Using '<' instead of '<=' in second blank excludes age 19.

Forgetting quotes around 'Adult'.

Use < to check if age is less than 12 for 'Child'. Then <= 19 for 'Teen'. Else print 'Adult'.

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