Operators & Logic›Core· 35 min read

Operators

Do maths, join text and update values with JavaScript operators.

What you will learn

Use arithmetic operators
Join strings with +
Use assignment shortcuts

Arithmetic

Operator	Does	Example
`+`	Add (or join text)	`5 + 2` → 7
`-`	Subtract	`5 - 2` → 3
`*`	Multiply	`5 * 2` → 10
`/`	Divide	`6 / 2` → 3
`%`	Remainder (modulo)	`7 % 2` → 1
`**`	Power	`2 ** 3` → 8

Let us put * (multiply) and + (join) to work in one small price calculation.

Arithmetic + string join

<script>
  let price = 100;
  let qty = 3;
  let total = price * qty;
  document.write("Total: ₹" + total);
</script>

Live preview

price * qty multiplies 100 by 3 and stores 300 in total. Then "Total: ₹" + total joins the label text to that number, so the page shows the finished sentence.

Note: Output: Total: ₹300

Assignment shortcuts

Update a variable using its own value: +=, -=, *=. And ++ adds one, -- subtracts one.

count += 3 and count++

<script>
  let count = 5;
  count += 3;   // same as count = count + 3  → 8
  count++;      // → 9
  document.write("Count is " + count);
</script>

Live preview

count starts at 5. count += 3 is a shortcut for "take whatever count is and add 3", making it 8. Then count++ adds just one more, making it 9. So the final printed value is 9.

Note: Output: Count is 9

Tip: The % (modulo) operator gives the remainder — perfect for checking even/odd: n % 2 === 0 means n is even.

Q. What does 7 % 3 give?

Answer: % is the remainder. 7 = 3×2 + 1, so 7 ÷ 3 leaves a remainder of 1.

✍️ Practice

Calculate the total cost of 4 items at ₹250 each and print it.
Use % to print whether the number 9 is even or odd (hint: 9 % 2).

🏠 Homework

Write a script that converts a temperature from Celsius to Fahrenheit (F = C * 9/5 + 32).