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How to work with numbers

Updated September 2026 · Beginner-friendly guide

Use arithmetic operators

JavaScript uses one number type for most integer and decimal arithmetic.

const subtotal = 12.5 * 3;
const shipping = 4;
const total = subtotal + shipping;
console.log(total);
console.log(17 % 5); // remainder: 2

Respect precedence

Multiplication and division happen before addition and subtraction. Parentheses make intent explicit.

console.log(2 + 3 * 4);   // 14
console.log((2 + 3) * 4); // 20
console.log(2 ** 3);      // 8

Round and format

Math provides numeric utilities. toFixed returns a string, which is useful for display but not continued arithmetic.

const value = 7.856;
console.log(Math.round(value));
console.log(Math.floor(value));
console.log(value.toFixed(2)); // "7.86"

Handle NaN and floating point

Invalid numeric operations may produce NaN. Decimal fractions can have tiny binary rounding differences.

const result = Number("not a number");
console.log(Number.isNaN(result)); // true
console.log(0.1 + 0.2);            // 0.30000000000000004
console.log((10 + 20) / 100);      // 0.3

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