JavaScript Math

`Math` is a namespace of static methods and constants for numeric work — rounding, comparison, exponents, randomness.

4 min read Level 1/5 #Math#numbers#random

What you'll learn

Round and floor/ceil with the right method
Generate random numbers in a range
Find min/max across an array

Math isn’t a constructor — it’s a frozen object of static functions and constants. You never new Math(). Just call Math.something(...).

Rounding

Method	Behavior
`Math.round(x)`	Round to nearest. `0.5` rounds UP
`Math.floor(x)`	Round DOWN to integer
`Math.ceil(x)`	Round UP to integer
`Math.trunc(x)`	Drop the fractional part (round toward zero)
`n.toFixed(d)`	Format with `d` decimals — returns a STRING

Rounding behavior script.js

console.log(Math.round(2.5));   // 3
console.log(Math.round(-2.5));  // -2  (rounds toward +∞ on .5)
console.log(Math.floor(2.9));   // 2
console.log(Math.ceil(2.1));    // 3
console.log(Math.trunc(-2.9));  // -2  (NOT -3)

console.log((1.005).toFixed(2)); // "1.00"  ← float-point gotcha

▶ Preview: console

Min, Max, Abs, Sign

min / max / abs / sign script.js

console.log(Math.min(3, 1, 2));      // 1
console.log(Math.max(3, 1, 2));      // 3
console.log(Math.abs(-7));           // 7
console.log(Math.sign(-7));          // -1  (-1, 0, or 1)

▶ Preview: console

For an array, spread it:

Max of an array script.js

const nums = [3, 1, 9, 4];
console.log(Math.max(...nums));   // 9

▶ Preview: console

Powers, Roots, Logs

Exponents and roots script.js

console.log(Math.pow(2, 8));     // 256       (or 2 ** 8)
console.log(Math.sqrt(81));      // 9
console.log(Math.cbrt(27));      // 3
console.log(Math.log2(1024));    // 10
console.log(Math.log10(1000));   // 3

▶ Preview: console

** is the operator form of Math.pow and is usually what you’ll reach for.

Random

Math.random() returns a number in [0, 1) (zero included, one excluded).

Random integer in a range script.js

// Random int in [min, max] inclusive
function randInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

console.log(randInt(1, 6));   // 1..6 — a die roll

▶ Preview: console

Constants Worth Knowing

Constant	Value
`Math.PI`	π
`Math.E`	Euler’s number
`Math.LN2`	ln(2)
`Math.LN10`	ln(10)

Trig (Briefly)

Angles are in radians, not degrees. Multiply by Math.PI / 180 to convert.

const deg = 90;
const rad = deg * Math.PI / 180;
console.log(Math.sin(rad));   // 1

Up Next

You’ve seen the language. The last stop is a quick tour of useful browser-platform APIs you’ll meet in real apps.

JavaScript Web APIs Tour →