Random

Number

Generate float

Between 0 (inclusive) and 1 (exclusive).

> Math.random()

Generate integer up to max

Generate between 0 and a max.

> Math.round(Math.random() * 1000)
// 123

Generate random float in range

> Math.random() * (max - min) + min;

As a function:

function getRandomArbitrary(min, max) {
  return Math.random() * (max - min) + min;
}

// 0 -> 10
Math.floor(Math.random() * 11);

// 1 -> 10
Math.floor(Math.random() * 10) + 1;

// 5 -> 20
Math.floor(Math.random() * 16) + 5;

// -10 -> (-2)
Math.floor(Math.random() * 9) - 10;

Get random integer between two values

From the Mozilla docs.

Min inclusive and max exclusive.

function getRandomInt(min, max) {
  min = Math.ceil(min);
  max = Math.floor(max);
  return Math.floor(Math.random() * (max - min)) + min;
}

For above:

It might be tempting to use Math.round() to accomplish that, but doing so would cause your random numbers to follow a non-uniform distribution, which may not be acceptable for your needs.

Inclusive for both.

function getRandomIntInclusive(min, max) {
  min = Math.ceil(min);
  max = Math.floor(max);
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

From source. This is simper than above as it lacks the rounding of min and max.

Inclusive for both.

function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1) + min);
}

Binary

Use .substring(start, end) to drop 0. at the start.

> Math.random().toString(2).substring(2)
// "00011111010001100100011010011111010011001101110001"

Random text

32-bit text.

> Math.random().toString(32).substr(2, 4)
"392l"

Get random element in an array

source

var item = myArray[Math.floor(Math.random()*myArray.length)];