JavaScript Number: integers, floats, and Math

Examples:

let number = 10;
let number = 1.4;

Additional data types:

Working with math:

Math.round();
Math.floor(); // Round down to the nearest integer (drops the fractional part).

Random numbers

Math.random() returns a floating-point number in the range [0, 1) — always less than 1, never exactly 1:

Math.random();

Scale the range by multiplying. Example — a number from 0 to 10 (not including 10):

Math.random() * 10;

For an integer index into an array of length n, multiply by n and floor:

Math.floor(Math.random() * 4); // 0, 1, 2, or 3
Math.floor(Math.random() * arr.length);

Useful functions:

const number = parseInt(someString);
const number = parseFloat(someString);
const thisIsNotANumber = isNaN(someVariable);

Convert string to number:

const s = '5';
const number = +s;
// or:
const number = +'5';

Number('15');   // We will get a number type.
+'15';          // We will get a number type.