Output using console.log in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does console.log() do in JavaScript?

console.log() prints messages or values to the browser's console. It's like writing a note to yourself to check what your program is doing.

beginner

How do you print the text "Hello, world!" using console.log()?

Use console.log('Hello, world!'); to show the message in the console.

beginner

Can console.log() print numbers and variables?

<p>Yes! You can print numbers like <code>console.log(123);</code> or variables like <code>let x = 5; console.log(x);</code>.</p>

beginner

What will this code print?

console.log(2 + 3);

It will print 5 because it adds the two numbers and shows the result.

beginner

Why is console.log() useful when learning to code?

It helps you see what your program is doing step-by-step, like checking your work on a homework problem.

What does console.log('Hi!'); do?

A Stops the program

B Saves 'Hi!' to a file

C Prints 'Hi!' to the console

D Shows a popup message

console.log() prints messages to the console, so it will show 'Hi!'.

Which is the correct way to print the number 10?

A console.log('10');

B console.log(10);

C console.print(10);

D print.console(10);

Use console.log(10); to print the number 10 as a number, not as text.

What will console.log(4 * 5); output?

A 20

B 45

C 9

D Error

It multiplies 4 by 5 and prints 20.

How do you print the value of a variable name?

A console.print(name);

B console.log('name');

C print(name);

D console.log(name);

Use console.log(name); to print the variable's value, not the word 'name'.

Which of these is NOT true about console.log()?

A It can create popup alerts

B It can print numbers

C It can print variables

D It can print strings

console.log() prints to the console, it does not create popup alerts.

Explain how console.log() helps you see what your JavaScript program is doing.

Think about how you check your work when solving a problem.

Describe how to use console.log() to print a variable and a message together.

Try combining text and variables inside console.log.

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