Assignment operators in Javascript

Introduction

Assignment operators help you store or update values in variables easily.

When you want to save a value in a box (variable).

When you want to add or subtract a number from what is already saved.

When you want to multiply or divide a value and keep the result in the same box.

When you want to combine text and save it back to the same variable.

When you want to quickly update a variable without writing it twice.

Syntax

Javascript

variable = value;
variable += value;
variable -= value;
variable *= value;
variable /= value;
variable %= value;
variable **= value;

The = operator sets a value.

Other operators like += add and assign in one step.

Examples

Add 5 to score and save it back to score.

Javascript

let score = 10;
score += 5;  // score is now 15

Combine strings and save the result.

Javascript

let text = 'Hi';
text += ' there!';  // text is now 'Hi there!'

Subtract 4 from count and update it.

Javascript

let count = 20;
count -= 4;  // count is now 16

Raise total to the power of 3 and save it.

Javascript

let total = 3;
total **= 3;  // total is now 27

Sample Program

This program shows how assignment operators change the value of points step by step.

Javascript

let points = 10;
console.log('Initial points:', points);

points += 5;
console.log('After adding 5:', points);

points *= 2;
console.log('After doubling:', points);

points -= 4;
console.log('After subtracting 4:', points);

points /= 2;
console.log('After dividing by 2:', points);

Important Notes

Assignment operators save time by combining math and assignment in one step.

Be careful with division and subtraction to avoid unexpected results.

Strings can be combined using += just like numbers.

Summary

Assignment operators store or update values in variables.

They combine math or text operations with saving the result.

Using them makes your code shorter and easier to read.

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