多次查找数组中相同元素的索引

Question

I'd like to find an element's POSITIONS in same array without methods, with an algorithm...

Example :

var a = [1,2,2,1,4,5,6]
to display positions of 1 : position 0 and 3
to display positions of 2 : position 1 and 2

What I have done so far:

function count(array,element){
    while(element in array){
        return array.indexOf(element);
    }
}

Answer 1

For getting all positions, you must walk whole array before return

var a = [1,2,2,1,4,5,6]

function count(array,element){
  var counts = [];
    for (i = 0; i < array.length; i++){
      if (array[i] === element) {  
        counts.push(i);
      }
    }
  return counts;
}

count(a, 1); //returns [0,3]
count(a, 2); //returns [1,2]

Answer 2

I'd suggest:

count (haystack, needle) {
    return haystack.filter(function (el, index) {
        if (el === needle) {
            return index;
        }
    });
}