1Math.random() 
2// will return a number between 0 and 1, you can then time it up to get larger numbers.
3//When using bigger numbers remember to use Math.floor if you want it to be a integer
4Math.floor(Math.random() * 10) // Will return a integer between 0 and 9
5Math.floor(Math.random() * 11) // Will return a integer between 0 and 10
6
7// You can make functions aswell 
8function randomNum(min, max) {
9	return Math.floor(Math.random() * (max - min)) + min; // You can remove the Math.floor if you don't want it to be an integer
10}

1function getRandomNumberBetween(min,max){
2    return Math.floor(Math.random()*(max-min+1)+min);
3}
4
5//usage example: getRandomNumberBetween(20,400); 
6

1function randomNumber(min, max) {
2  return Math.floor(Math.random() * (max - min)) + min + 1;
3}

1Math.floor(Math.random() * 10);

1function getRandomNumberBetween(min,max){
2    return Math.floor(Math.random()*(max-min+1)+min);
3}
4getRandomNumberBetween(50,80);
5
6

1(Math.random()*100).toFixed(0)