Output using console.log in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of console.log with template literals

What is the output of this code?

const name = "Alice";
const age = 30;
console.log(`Name: ${name}, Age: ${age}`);

Javascript

const name = "Alice";
const age = 30;
console.log(`Name: ${name}, Age: ${age}`);

A Name: Alice Age: 30

B Name: name, Age: age

C Name: ${name}, Age: ${age}

D Name: Alice, Age: 30

💡 Hint

Look how template literals use ${} to insert variables inside backticks.

The template literal replaces ${name} and ${age} with their variable values inside the string.

❓ Predict Output

intermediate

Output of console.log with multiple arguments

What will this code print?

console.log("Hello", "World", 2024);

Javascript

console.log("Hello", "World", 2024);

A Hello World 2024

B Hello, World, 2024

C HelloWorld2024

D "Hello World 2024"

💡 Hint

console.log prints each argument separated by spaces.

console.log prints all arguments separated by spaces without quotes.

❓ Predict Output

advanced

Output of console.log with undefined variable

What happens when you run this code?

let x;
console.log(x);

Javascript

let x;
console.log(x);

A 0

B null

C undefined

D ReferenceError

💡 Hint

Variables declared but not assigned have a special value.

A declared variable without a value is undefined in JavaScript.

❓ Predict Output

advanced

Output of console.log with object and array

What will this code print?

const obj = {a: 1, b: 2};
const arr = [3, 4];
console.log(obj, arr);

Javascript

const obj = {a: 1, b: 2};
const arr = [3, 4];
console.log(obj, arr);

A { a: 1, b: 2 } [ 3, 4 ]

B [object Object] [3,4]

C {a:1,b:2},[3,4]

D a:1,b:2 3,4

💡 Hint

console.log prints objects and arrays in readable form separated by spaces.

console.log prints the object and array as their readable forms separated by space.

🧠 Conceptual

expert

Behavior of console.log with asynchronous code

What is the output order of this code?

console.log('Start');
setTimeout(() => console.log('Timeout'), 0);
console.log('End');

Javascript

console.log('Start');
setTimeout(() => console.log('Timeout'), 0);
console.log('End');

A End\nStart\nTimeout

B Start\nEnd\nTimeout

C Timeout\nStart\nEnd

D Start\nTimeout\nEnd

💡 Hint

setTimeout with 0 delay runs after current code finishes.

The synchronous logs run first, then the setTimeout callback runs after the current call stack is empty.

Practice

1. What does console.log do in JavaScript?

easy

A. It creates a new variable.

B. It stops the program from running.

C. It prints messages or values to the console.

D. It reads input from the user.

Solution

1. Step 1: Understand the purpose of console.log

   console.log is used to show messages or values in the console, helping to see what the program does.

2. Step 2: Compare options with the purpose

   Only It prints messages or values to the console. matches this purpose. Other options describe different actions.

3. Final Answer:

   It prints messages or values to the console. -> Option C

4. Quick Check:

   console.log prints output [OK]

Hint: Remember: console.log shows info in the console [OK]

Common Mistakes:

• Thinking console.log stops the program
• Confusing console.log with input functions
• Assuming console.log creates variables

2. Which of the following is the correct syntax to print "Hello World" using console.log?

easy

A. console.log: 'Hello World'

B. console.print('Hello World')

C. print.console('Hello World')

D. console.log('Hello World')

Solution

1. Step 1: Identify correct console.log syntax

   The correct way to print is console.log('text') with parentheses and quotes around the text.

2. Step 2: Check each option

   console.log('Hello World') uses correct syntax. Options A, B, and C use wrong method names or punctuation.

3. Final Answer:

   console.log('Hello World') -> Option D

4. Quick Check:

   console.log('text') is correct syntax [OK]

Hint: Use console.log() with parentheses and quotes [OK]

Common Mistakes:

• Using console.print instead of console.log
• Missing parentheses
• Using colon instead of parentheses

3. What will be the output of the following code?

let x = 5;
let y = 10;
console.log(x + y);

medium

A. 15

B. 510

C. x + y

D. undefined

Solution

1. Step 1: Understand the variables and operation

   Variables x and y hold numbers 5 and 10. The expression x + y adds these numbers.

2. Step 2: Calculate the sum

   5 + 10 equals 15, so console.log(x + y) prints 15.

3. Final Answer:

   15 -> Option A

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: Add numbers inside console.log to get sum [OK]

Common Mistakes:

• Thinking + concatenates as strings here
• Printing variable names instead of values
• Expecting undefined output

4. Find the error in this code:

console.log('Hello World'

medium

A. Missing closing parenthesis

B. Missing semicolon

C. Wrong quotes used

D. console.log is not a function

Solution

1. Step 1: Check the syntax of console.log

   The function call must have matching opening and closing parentheses.

2. Step 2: Identify the missing part

   The code misses the closing parenthesis after the string, causing a syntax error.

3. Final Answer:

   Missing closing parenthesis -> Option A

4. Quick Check:

   Parentheses must match in function calls [OK]

Hint: Count opening and closing parentheses carefully [OK]

Common Mistakes:

• Ignoring missing parenthesis
• Thinking semicolon is mandatory error
• Confusing quotes with parentheses

5. What will this code print?

let a = 3;
let b = '4';
console.log(a + b);

hard

A. 7

B. 34

C. undefined

D. TypeError

Solution

1. Step 1: Understand the types of variables

   Variable a is a number 3, b is a string '4'.

2. Step 2: Apply + operator with mixed types

   When adding number + string, JavaScript converts number to string and concatenates, so 3 + '4' becomes '34'.

3. Final Answer:

   34 -> Option B

4. Quick Check:

   Number + string concatenates as string [OK]

Hint: Number + string joins as text, not sums [OK]

Common Mistakes:

• Expecting numeric sum
• Thinking it causes error
• Ignoring type conversion rules