Math.random()
used when generating random numbers of a range. Many times Math.random()
used in conjunction with another method such as Math.floor()
or user input to get a whole number at the end.

case 1) Generate whole number ranging from
[0, 3]
(numbers from 0 to 3 both ends inclusive). Math.random() generates pseudorandom number in the range 0 to less than 1 (inclusive of 0, but not 1).
 To only get whole numbers, we use Math.floor() to round down.
// multiply by 4; Math.random()'s upper end, 4 is exclusive
const randomNumber = Math.floor(Math.random() * 4);

case 2) Generate whole number
[1, 6]
(numbers from 1 to 6 both ends inclusive). Add one to randomly generated numbers.
 Math.ceil() may look simple to use here but it will generate 0 as a result if Math.random() give 0.
// => `[0, 6]`
Math.ceil(Math.random() * 6)
 We want
[1,6]
// => `[1, 6]`
// Math.random() * 6 => [0, 5] then add one to each => [1, 6]
Math.floor(Math.random() * 6 + 1)
 case 3) Generate whole number from 1 to user's favorite whole number.
const userFavNum = 5;
// Math.random() * 5 => [0, 4] then add one to each => [1, 5]
Math.floor((Math.random() * userFavNum) + 1)
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