The Math Object: A Calculator in Your Pocket

JavaScript comes with a built-in toolbox called Math, packed with useful math functions. You use them by writing Math. followed by the tool's name.

Rounding numbers

console.log(Math.round(4.5));
console.log(Math.round(4.4));
console.log(Math.floor(4.9));
console.log(Math.ceil(4.1));
console.log(Math.trunc(-4.7));

5
4
4
5
-4

Other handy tools

console.log(Math.max(4, 19, 7, 2));
console.log(Math.min(4, 19, 7, 2));
console.log(Math.abs(-15));
console.log(Math.sqrt(81));
console.log(Math.PI);

19
2
15
9
3.141592653589793

• Math.max(...) and Math.min(...) find the biggest and smallest of any numbers you give them.
• Math.abs(x) gives the absolute value, which means it removes the minus sign. Useful for "how far apart are these two numbers?"
• Math.sqrt(x) gives the square root.
• Math.PI is the number π. (Note: no parentheses! It's a value, not an action.)

Random numbers

Now for the fun one. Math.random() gives you a random decimal number between 0 (included) and 1 (not included). Every time you call it, you get a different number:

console.log(Math.random());
console.log(Math.random());

0.7341858224108491
0.0286427493216813

(Your numbers will be different. That's the whole point!)

A random decimal between 0 and 1 isn't very useful on its own. But with a bit of math, we can turn it into a random whole number in any range we like. Here's how to simulate rolling a six-sided die:

const roll = Math.floor(Math.random() * 6) + 1;
console.log(roll);

Let's walk through it, step by step:

1. Math.random() gives a number from 0 up to (but not including) 1, like 0.734.
2. * 6 stretches it to a number from 0 up to (but not including) 6, like 4.404.
3. Math.floor(...) rounds down to a whole number from 0 to 5, like 4.
4. + 1 shifts it to a number from 1 to 6, like 5. 🎲

Math.floor(Math.random() * max) + 1