Sorting an Array in Random Order

You used

var as = ["max","jack","sam"];  
var s = as.sort(func);  

function func(a, b) {  
  return 0.5 - Math.random();
}  

console.log(s);

And here the most important thing is as.sort(func).
func(a,b) will return value in range of [-0.5,0.5].

Because this function return 0.5 - Math.random() and Math.random() will return the float value which is in range of [0,1].
So that your func will return value in range of [-0.5,0.5].

And this mean that sort order will be set increase or decrease. this is random. So your result will be random

var as = ["max","jack","sam"];  
var s = as.sort(func);  

function func(a, b) {  
  return Math.random();
}  

console.log(s);

var as = ["max","jack","sam"];  
var s = as.sort(func);  

function func(a, b) {  
  return 0 - Math.random();
}  

console.log(s);

var as = ["max","jack","sam"];  
var s = as.sort(func);  

function func(a, b) {  
  return 0.5 - Math.random();
}  

console.log(s);

Math.random() returns a number between 0 and 1 (exclusive). We're using 0.5 because it is the mean value.

Array.sort() sorts the parameters based on the return value. So, 0.5 - Math.random() will yield either positive or negative value with equal probability. Hence, it will sort the parameters randomly.

How it really works

• If the return value of Array.sort() is positive, then the index of the first parameter will be higher than that of the second.
• If it is negative, then the index of the second parameter will be higher than that of the first.
• And, if it is 0, then do nothing.

Math.random() return random value between 0 to 1 (0 is included but 1 is excluded). So 0.5 act as mid point. If use use value like greater than 1 or less 0 than it will always be either true or false. So for this reason 0.5 is used.

You can read more here about Math.random()

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random

Let's understand it bit more with examples

var as = ["max","jack","sam"];  
var s = as.sort(func);  

function func(a, b) {  
  return 0.5 - Math.random();
}  

console.log(s);

This is what you get when you use value greater than 1

var as = ["max","jack","sam"];  
var s = as.sort(func);  

function func(a, b) {  
  return 1 - Math.random();
}  

console.log(s);

This is what happens when you use value less than 0

var as = ["max","jack","sam"];  
var s = as.sort(func);  

function func(a, b) {  
  return -1 - Math.random();
}  

console.log(s);

P.S :-

1. Try printing output from all the above condition you will see that last two condition will always return either true or false from function. so you will not get a random sorting.

2. Now talk about any value from 0 to 0.99 you can use any value but 0.5 will serve your purpose best.Because it's a middle point you're most likely to get best answer.