how do you make a random array in javascript

var arr = [];
while(arr.length < 8){
    var r = Math.floor(Math.random() * 100) + 1;
    if(arr.indexOf(r) === -1) arr.push(r);
}
console.log(arr);// how to generate random words from an array
const Coins = ["Heads","Tails"]
let Generate = Math.floor((Math.random() * Coins.length));

console.log(Coins[Generate]) // this will print the outcome//This example is to generate an array with 40 random elements, with random values from 0 to 39 

for (var a=[],i=0;i<40;++i) a[i]=i;

// http://stackoverflow.com/questions/962802#962890
function shuffle(array) {
  var tmp, current, top = array.length;
  if(top) while(--top) {
    current = Math.floor(Math.random() * (top + 1));
    tmp = array[current];
    array[current] = array[top];
    array[top] = tmp;
  }
  return array;
}

a = shuffle(a);