JS Arithmetic

JavaScript Arithmetic: Operations, Remainders, and Precision

JavaScript arithmetic operators perform mathematical calculations on numbers, including addition (+), subtraction (-), multiplication (*), division (/), remainder (%), and exponentiation (**).

Arithmetic Operators Reference

Prefix vs. Postfix Increment (++)

Both ++x and x++ add 1 to a number, yet they return different values inside larger expressions. Prefix ++x increments first and returns the new value, whereas postfix x++ returns the old value before incrementing.

let page = 1;
console.log("Postfix returns old:", page++); // 1, then page becomes 2
console.log("Prefix returns new:", ++page);  // 3

// Safe currency math using integer cents
const itemCents = 10 + 20;
const dollars = itemCents / 100;
console.log("Exact dollars:", dollars); // 0.3

Handling Floating-Point Math

JavaScript stores numbers in 64-bit binary floating-point format, so 0.1 + 0.2 evaluates to 0.30000000000000004. For money and invoices, convert amounts to integer cents before adding or multiplying, then divide by 100 at display time.

Common Mistakes to Avoid

• Adding strings and numbers with +: "5" + 2 produces "52" because + concatenates whenever either side is a string. Convert inputs with Number(value) first.
• Assuming / drops decimals: Unlike Java or C integer division, 5 / 2 in JavaScript returns 2.5. Use Math.trunc(5 / 2) when you need a whole integer.
• Forgetting % sign rules: In JavaScript, -7 % 3 returns -1, matching the sign of the left dividend.

Frequently Asked Questions

What happens when I divide by zero in JavaScript?

Dividing a positive number by 0 returns Infinity, dividing a negative number by 0 returns -Infinity, and 0 / 0 returns NaN (Not a Number).

How do I calculate powers without Math.pow()?

Use the ES2016 exponentiation operator **, such as 3 ** 2 for 9 or 16 ** 0.5 for square root 4.

How can I check if an integer is even or odd?

Check the remainder after dividing by 2: num % 2 === 0 is true for even integers.