Assignment operators in Javascript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code using += operator?

Consider the following JavaScript code snippet. What will be printed to the console?

Javascript

let x = 5;
x += 3;
console.log(x);

A 5

B 8

C 3

D 53

💡 Hint

Remember that += adds the right value to the left variable.

The += operator adds the right value (3) to the left variable (5), so x becomes 8.

❓ Predict Output

intermediate

What is the output after using *= operator?

Look at this code. What will be the value of y after execution?

Javascript

let y = 4;
y *= 2;
console.log(y);

A 6

B 42

C 8

D 2

💡 Hint

The *= operator multiplies the variable by the right value.

y starts at 4, then y *= 2 multiplies it by 2, so y becomes 8.

❓ Predict Output

advanced

What is the output of this code using combined operators?

What will be printed to the console after running this code?

Javascript

let a = 10;
a -= 3;
a /= 7;
console.log(a.toFixed(2));

A 11

B 2

C 0

D 1.00

💡 Hint

Apply each operator step by step and then format the number.

a starts at 10, a -= 3 makes it 7, then a /= 7 makes it 1. toFixed(2) formats it as '1.00'.

❓ Predict Output

advanced

What is the output of this code using %= operator?

What will be the value of b after this code runs?

Javascript

let b = 15;
b %= 4;
console.log(b);

A 3

B 4

C 15

D 11

💡 Hint

The %= operator gives the remainder of division.

15 divided by 4 leaves a remainder of 3, so b becomes 3.

❓ Predict Output

expert

What is the output of this tricky assignment code?

What will be printed to the console after running this code?

Javascript

let c = 2;
let d = 3;
c *= d += 4;
console.log(c);

A 14

B 10

C 8

D 6

💡 Hint

Remember that d += 4 happens first, then c *= d.

d += 4 makes d = 7, then c *= 7 makes c = 14.

Practice

1. What does the assignment operator += do in JavaScript?

easy

A. Adds the right value to the left variable and updates the variable

B. Subtracts the right value from the left variable

C. Assigns the right value to the left variable without change

D. Multiplies the left variable by the right value

Solution

1. Step 1: Understand the += operator

   The += operator adds the value on the right to the variable on the left.

2. Step 2: Effect on the variable

   It updates the left variable with the new sum, combining addition and assignment.

3. Final Answer:

   Adds the right value to the left variable and updates the variable -> Option A

4. Quick Check:

   x += y means x = x + y [OK]

Hint: Think: add then save back to the same variable [OK]

Common Mistakes:

• Confusing += with simple assignment =
• Thinking it subtracts or multiplies
• Believing it only adds without updating

2. Which of the following is the correct syntax to multiply a variable num by 5 and update it using an assignment operator?

easy

A. num =* 5;

B. num = *5;

C. num *= 5;

D. num = 5*;

Solution

1. Step 1: Identify the correct multiplication assignment syntax

   The correct operator to multiply and assign is *=, placed between variable and value.

2. Step 2: Check each option

   num *= 5; uses num *= 5; which is valid syntax. Others have incorrect operator placement or invalid syntax.

3. Final Answer:

   num *= 5; -> Option C

4. Quick Check:

   Use *= for multiply and assign [OK]

Hint: Remember operator goes between variable and value, no spaces inside [OK]

Common Mistakes:

• Writing =* instead of *=
• Adding spaces inside operator
• Using invalid symbols like 5*;

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

let x = 10;
x -= 3;
console.log(x);

medium

A. 13

B. 7

C. 3

D. 10

Solution

1. Step 1: Understand the initial value and operation

   Variable x starts at 10. The operator -= subtracts 3 from x.

2. Step 2: Calculate the new value

   10 - 3 = 7, so x becomes 7.

3. Final Answer:

   7 -> Option B

4. Quick Check:

   x -= 3 means x = x - 3 [OK]

Hint: Subtract then save result back to variable [OK]

Common Mistakes:

• Adding instead of subtracting
• Printing old value before update
• Confusing -= with =-

4. Find the error in this code snippet:

let count = 5;
count +== 2;
console.log(count);

medium

A. Console.log should be console.print

B. Variable count is not declared

C. Missing semicolon after declaration

D. The operator +== is invalid syntax

Solution

1. Step 1: Identify the operator used

   The code uses +== which is not a valid assignment operator in JavaScript.

2. Step 2: Correct operator usage

   The correct operator to add and assign is +=. So it should be count += 2;.

3. Final Answer:

   The operator +== is invalid syntax -> Option D

4. Quick Check:

   Use += not +== for addition assignment [OK]

Hint: Assignment operators have one = sign only [OK]

Common Mistakes:

• Using double equals with + (like +==)
• Confusing console.log with other functions
• Ignoring semicolon errors (usually optional)

5. Given the code below, what will be the final value of result?

let result = 2;
result *= 3;
result += 4;
result /= 2;

hard

A. 5

B. 7

C. 8

D. 10

Solution

1. Step 1: Multiply result by 3

   Starting with result = 2, after result *= 3, result becomes 6.

2. Step 2: Add 4 to result

   After result += 4, result becomes 6 + 4 = 10.

3. Step 3: Divide result by 2

   After result /= 2, result becomes 10 / 2 = 5.

4. Final Answer:

   5 -> Option A

5. Quick Check:

   2 * 3 + 4 then / 2 = 5 [OK]

Hint: Follow each operator step-by-step to update variable [OK]

Common Mistakes:

• Doing operations in wrong order
• Forgetting to update variable after each step
• Mixing up division and multiplication