JavaScript Math

Math is already there

Python starts with import math. JavaScript does not. Math is a built-in object on the global scope. Call Math.round(n) from any script in the browser.

You never write new Math(). The functions live on the object itself. Constants such asMath.PI live there too.

round, floor, and ceil

Math.round(n) goes to the nearest integer. Halfway cases such as 2.5 round toward +Infinity, so 2.5 becomes 3.

Math.floor(n) goes down (toward −Infinity). Math.ceil(n) goes up (toward +Infinity). For positive numbers, floor chops the fraction and ceil takes the next integer if any fraction exists.

console.log(Math.round(2.3));
console.log(Math.round(2.7));
console.log(Math.floor(2.7));
console.log(Math.ceil(2.1));
console.log(Math.floor(-1.2));

document.body.textContent =
  Math.round(2.7) + " " + Math.floor(2.7) + " " + Math.ceil(2.1);

max and min

Math.max(a, b, ...) returns the largest argument. Math.min returns the smallest. Pass as many numbers as you need. With no arguments, max is -Infinity andmin is Infinity.

To rank an array, spread is not required yet: Math.max.apply(null, list) works, or loop and keep a running best. Empty lists are a special case — do not call max on nothing by accident.

const scores = [88, 41, 95, 70];
const high = Math.max(88, 41, 95, 70);
const low = Math.min(88, 41, 95, 70);

console.log(high);
console.log(low);
console.log(Math.max(0, high));

document.body.textContent = "high " + high + " / low " + low;

abs, pow, and sqrt

Math.abs(n) drops the sign: negative becomes positive. Use it for distances and differences.Math.pow(base, exp) raises a power. base ** exp is the same idea with an operator.Math.sqrt(n) is the square root.

console.log(Math.abs(-12));
console.log(Math.pow(2, 8));
console.log(2 ** 8);
console.log(Math.sqrt(9));

const a = 3;
const b = 4;
const c = Math.sqrt(a * a + b * b);
console.log(c);

document.body.textContent = "hypot " + c;

The usual toolkit

Rounding for display is often Number(n.toFixed(2)) from the number-methods chapter, notMath.round. round has no “decimal places” argument.

What to remember

• No import. Call Math.method(...) directly.
• floor goes down, ceil goes up, round goes to nearest.
• max and min take separate arguments, not one array, in the basic form.
• Do not write new Math().

Next: random numbers — scale a float in [0, 1) into an integer range.