Why operators are needed in Javascript - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add two numbers and store the result in sum.

Javascript

let a = 5;
let b = 3;
let sum = a [1] b;

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

A*

B-

C/

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction - instead of addition +.

The + operator adds two numbers together.

2fill in blank

medium

Complete the code to check if age is greater than 18.

Javascript

let age = 20;
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 less than < instead of greater than >.

The > operator checks if the left value is greater than the right value.

3fill in blank

hard

Fix the error in the code to multiply x and y.

Javascript

let x = 4;
let y = 7;
let product = x [1] y;

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

A*

B-

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition + or subtraction - instead of multiplication *.

The * operator multiplies two numbers.

4fill in blank

hard

Fill both blanks to create an object with keys as uppercase letters and values as numbers greater than 10.

Javascript

const data = {
  [1]: 15,
  [2]: 20
};

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

A'A'

B'b'

C'B'

D'a'

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase letters when uppercase is required.

Not using quotes around keys.

Keys in objects are strings. Using uppercase letters 'A' and 'B' as keys matches the requirement.

5fill in blank

hard

Fill both blanks to create a condition that checks if score is between 50 and 100 (inclusive).

Javascript

if (score [1] 50 && score [2] 100) {
  console.log('Pass');
} else {
  console.log('Fail');
}

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

A>=

B<=

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using > or < without equals, missing boundary values.

The condition uses >= to check if score is at least 50 and <= to check if score is at most 100.

Practice

1.

Why do we need operators in JavaScript?

Choose the best reason.

easy

A. To perform calculations and compare values

B. To create new variables automatically

C. To write comments in the code

D. To change the color of the webpage

Solution

1. Step 1: Understand the role of operators

   Operators are symbols that let us do math like adding or compare values like checking if one number is bigger than another.

2. Step 2: Eliminate unrelated options

   Creating variables, writing comments, or changing colors are not done by operators but by other parts of JavaScript or CSS.

3. Final Answer:

   To perform calculations and compare values -> Option A

4. Quick Check:

   Operators = calculations and comparisons [OK]

Hint: Operators do math and comparisons in code [OK]

Common Mistakes:

• Thinking operators create variables
• Confusing operators with comments
• Believing operators change webpage style

2.

Which of these is the correct way to add two numbers a and b in JavaScript?

easy

A. a plus b

B. a + b

C. a & b

D. a - b

Solution

1. Step 1: Identify the addition operator

   In JavaScript, the plus sign + is used to add two numbers.

2. Step 2: Check each option

   a plus b uses words which is invalid syntax. a & b uses & which is a bitwise AND operator, not addition. a - b uses minus - which subtracts.

3. Final Answer:

   a + b -> Option B

4. Quick Check:

   Addition operator = + [OK]

Hint: Use + sign to add numbers in JavaScript [OK]

Common Mistakes:

• Writing words instead of symbols
• Using & instead of +
• Confusing subtraction with addition

3.

What will be the output of this code?

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

medium

A. true

B. 5

C. false

D. 10

Solution

1. Step 1: Understand the comparison operator

   The operator > checks if the left value is greater than the right value.

2. Step 2: Compare the values of x and y

   Since x = 5 and y = 10, 5 is not greater than 10, so the expression x > y is false.

3. Final Answer:

   false -> Option C

4. Quick Check:

   5 > 10 = false [OK]

Hint: Compare values carefully with > or < [OK]

Common Mistakes:

• Assuming 5 is greater than 10
• Confusing output with variable values
• Mixing up true and false

4.

Find the error in this code snippet:

let a = 7;
let b = 3;
let result = a * b;
console.log(result);

Why is the output not showing the product?

medium

A. The multiplication operator is wrong

B. Variables a and b are not declared

C. Missing semicolon after console.log

D. No error, code works fine

Solution

1. Step 1: Check operator and variables

   The operator * correctly multiplies a and b. Both variables are declared with let.

2. Step 2: Verify syntax and output

   Semicolons are optional in JavaScript and the code will output 21 correctly.

3. Final Answer:

   No error, code works fine -> Option D

4. Quick Check:

   Multiplication with * works fine [OK]

Hint: Check if operator and variables are declared properly [OK]

Common Mistakes:

• Thinking semicolon is mandatory
• Confusing * with another operator
• Assuming variables are undeclared

5.

You want to check if a number n is between 10 and 20 (inclusive). Which operator expression correctly does this?

hard

A. n >= 10 && n <= 20

B. n > 10 || n < 20

C. n > 10 && n < 20

D. n == 10 && n == 20

Solution

1. Step 1: Understand inclusive range check

   To include 10 and 20, use >= for 10 and <= for 20.

2. Step 2: Analyze each option

   n > 10 && n < 20 excludes 10 and 20 because it uses > and <. n > 10 || n < 20 uses OR which allows values outside the range. n == 10 && n == 20 checks if n equals both 10 and 20 simultaneously, which is impossible.

3. Final Answer:

   n >= 10 && n <= 20 -> Option A

4. Quick Check:

   Inclusive range uses >= and <= with AND [OK]

Hint: Use >= and <= with && for inclusive range checks [OK]

Common Mistakes:

• Using > and < excludes boundary values
• Using || instead of && allows wrong values
• Checking equality to two values at once