Ternary operator in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested ternary operator

What is the output of the following JavaScript code?

Javascript

const x = 5;
const y = 10;
const result = x > 3 ? (y < 15 ? 'A' : 'B') : 'C';
console.log(result);

A "B"

B "A"

C "C"

D undefined

💡 Hint

Check the conditions step by step starting from the outer ternary.

x is 5 which is greater than 3, so the outer condition is true. Then y is 10 which is less than 15, so the inner condition is true. Therefore, the result is 'A'.

❓ Predict Output

intermediate

Ternary operator with falsy values

What will be logged to the console?

Javascript

const value = 0;
const output = value ? 'Yes' : 'No';
console.log(output);

A "No"

B undefined

C 0

D "Yes"

💡 Hint

Remember how JavaScript treats 0 in boolean context.

0 is a falsy value in JavaScript, so the ternary condition evaluates to false and the output is 'No'.

❓ Predict Output

advanced

Ternary operator with side effects

What is the output of this code?

Javascript

let count = 0;
const result = count === 0 ? (count += 5) : (count += 10);
console.log(result, count);

A 5 0

B 10 10

C 0 5

D 5 5

💡 Hint

Check how the ternary operator changes the count variable.

count starts at 0, so the condition is true. The expression (count += 5) adds 5 to count and returns 5. Both result and count become 5.

❓ Predict Output

advanced

Ternary operator with different types

What will this code print?

Javascript

const a = true;
const b = false;
const output = a ? (b ? 1 : 'two') : 3;
console.log(typeof output, output);

A "string two"

B "number 1"

C "number 3"

D "boolean true"

💡 Hint

Evaluate the nested ternary carefully and check the type of the final value.

a is true, so we check b. b is false, so the inner ternary returns 'two' which is a string. The typeof output is 'string'.

🧠 Conceptual

expert

Understanding ternary operator evaluation order

Consider the code below. What is the value of variable result after execution?

Javascript

let x = 2;
const result = x > 1 ? x++ : --x;

A 1

B 3

C 2

D SyntaxError

💡 Hint

Remember that x++ returns the value before incrementing.

x is 2 which is greater than 1, so the condition is true. The expression x++ returns 2 (the current value) and then increments x to 3. So result is 2, but x becomes 3.

Practice

1. What does the ternary operator condition ? expr1 : expr2 do in JavaScript?

easy

A. Executes both expr1 and expr2 and returns their sum.

B. Always returns expr2 regardless of the condition.

C. Throws an error if condition is false.

D. Returns expr1 if condition is true, otherwise returns expr2.

Solution

1. Step 1: Understand the ternary operator structure

   The ternary operator has the form condition ? expr1 : expr2. It checks the condition.

2. Step 2: Determine the returned value based on the condition

   If the condition is true, it returns expr1. Otherwise, it returns expr2.

3. Final Answer:

   Returns expr1 if condition is true, else expr2 -> Option D

4. Quick Check:

   condition ? expr1 : expr2 = expr1 or expr2 [OK]

Hint: Remember: condition ? trueValue : falseValue [OK]

Common Mistakes:

• Thinking both expressions run always
• Confusing the order of expr1 and expr2
• Assuming it throws error on false condition

2. Which of the following is the correct syntax for using the ternary operator in JavaScript?

easy

A. condition ? expr1 : expr2;

B. condition ? expr1, expr2;

C. condition : expr1 ? expr2;

D. condition ? (expr1 : expr2);

Solution

1. Step 1: Recall the ternary operator syntax

   The correct syntax is condition ? expr1 : expr2 with a question mark and colon separating parts.

2. Step 2: Check each option for correct punctuation

   condition ? expr1 : expr2; matches the correct syntax. Options B, C, and D misuse commas, colons, or parentheses.

3. Final Answer:

   condition ? expr1 : expr2; -> Option A

4. Quick Check:

   Syntax is condition ? expr1 : expr2 [OK]

Hint: Look for ? and : in correct order with no extra symbols [OK]

Common Mistakes:

• Using commas instead of colon
• Swapping ? and :
• Adding unnecessary parentheses

3. What is the output of this code?

const age = 20;
const canVote = age >= 18 ? 'Yes' : 'No';
console.log(canVote);

medium

A. 'No'

B. 'Yes'

C. true

D. undefined

Solution

1. Step 1: Evaluate the condition age >= 18

   Since age is 20, which is greater than or equal to 18, the condition is true.

2. Step 2: Determine the value assigned to canVote

   Because the condition is true, canVote is assigned the string 'Yes'.

3. Final Answer:

   'Yes' -> Option B

4. Quick Check:

   20 >= 18 ? 'Yes' : 'No' = 'Yes' [OK]

Hint: Check condition result true or false to pick value [OK]

Common Mistakes:

• Confusing true and false branches
• Thinking it returns boolean true/false
• Ignoring the condition value

4. Find the error in this code snippet:

let score = 85;
let grade = score > 90 ? 'A' : score > 80 ? 'B' : 'C';
console.log(grade);

medium

A. The code is correct and will output 'B'.

B. Incorrect use of multiple ternary operators is not allowed.

C. Missing parentheses around nested ternary expressions.

D. The variable grade is not declared properly.

Solution

1. Step 1: Analyze the nested ternary expression

   The expression uses nested ternary operators without parentheses, which is allowed in JavaScript.

2. Step 2: Evaluate the condition with score = 85

   First condition score > 90 is false, so it checks score > 80, which is true, so grade is 'B'.

3. Final Answer:

   The code is correct and will output 'B'. -> Option A

4. Quick Check:

   Nested ternary without parentheses works [OK]

Hint: Nested ternary operators can be used without parentheses [OK]

Common Mistakes:

• Assuming nested ternary needs parentheses
• Thinking multiple ternaries are invalid syntax
• Confusing variable declaration errors

5. You want to assign a variable status based on a number score: if score is 0 or less, status should be 'Fail'; if between 1 and 50, 'Pass'; otherwise 'Excellent'. Which ternary expression correctly does this?

hard

A. const status = score <= 0 ? 'Fail' : (score > 50 ? 'Pass' : 'Excellent');

B. const status = score < 0 ? 'Fail' : score < 50 ? 'Pass' : 'Excellent';

C. const status = score <= 0 ? 'Fail' : score <= 50 ? 'Pass' : 'Excellent';

D. const status = score === 0 ? 'Fail' : score < 50 ? 'Pass' : 'Excellent';

Solution

1. Step 1: Understand the conditions for status

   score <= 0 means 'Fail', between 1 and 50 means 'Pass', and above 50 means 'Excellent'.

2. Step 2: Check each option against these conditions

   const status = score <= 0 ? 'Fail' : score <= 50 ? 'Pass' : 'Excellent'; correctly checks score <= 0 for 'Fail', then score <= 50 for 'Pass', else 'Excellent'. Others have wrong ranges or conditions.

3. Final Answer:

   const status = score <= 0 ? 'Fail' : score <= 50 ? 'Pass' : 'Excellent'; -> Option C

4. Quick Check:

   Correct ranges and order in ternary [OK]

Hint: Check conditions cover all ranges without gaps [OK]

Common Mistakes:

• Using wrong comparison operators
• Missing equal signs causing wrong ranges
• Incorrect order of conditions