generate random number array javascript from principal array

                                    //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);

                                    let numbers = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20],
    generated = [];
for (let i = 0; i < 10; i++)
{
    let random_index;
    while(!random_index)
    {
        let tmp = Math.floor(Math.random() * numbers.length);        
        if( !generated.filter( (g) => numbers[tmp] == g).length )
            random_index = tmp;
    }
    generated.push(numbers[random_index]);
}
console.log(generated);