Assignment operators in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add 5 to the variable num using an assignment operator.

Javascript

let num = 10;
num [1] 5;

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

A/=

B*=

C+=

D-=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+=' will subtract instead of add.

Using '*' or '/' will multiply or divide instead of adding.

The '+=' operator adds the value on the right to the variable on the left and assigns the result back to the variable.

2fill in blank

medium

Complete the code to multiply count by 3 using an assignment operator.

Javascript

let count = 4;
count [1] 3;

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

A+=

B*=

C-=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+=' will add instead of multiply.

Using '-=' or '/=' will subtract or divide instead of multiply.

The '*=' operator multiplies the variable by the value on the right and assigns the result back to the variable.

3fill in blank

hard

Fix the error in the code to subtract 2 from score using an assignment operator.

Javascript

let score = 15;
score [1] 2;

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

A-=

B*=

C+=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+=' will add instead of subtract.

Using '*=' or '/=' will multiply or divide instead of subtract.

The '-=' operator subtracts the value on the right from the variable and assigns the result back to the variable.

4fill in blank

hard

Fill both blanks to divide total by 4 and assign the result back to total.

Javascript

let total = 20;
total [1] [2];

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

A/=

B+=

C4

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+=' instead of '/=' will add instead of divide.

Using 2 instead of 4 will divide by the wrong number.

The '/=' operator divides the variable by the value on the right and assigns the result back. We divide by 4 here.

5fill in blank

hard

Fill all three blanks to increase value by 10, then multiply by 2, and finally subtract 5 using assignment operators.

Javascript

let value = 5;
value [1] 10;
value [2] 2;
value [3] 5;

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

A+=

B*=

C-=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of operators.

Using '/=' instead of '*=' or '-='.

First, '+=' adds 10 to value. Then '*=' multiplies value by 2. Finally, '-=' subtracts 5 from value.

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