Finding the positive numbers count in an ECMAScipt array All I am trying to achieve is better use of built-in ES functions.

var arr = [0, 1, 2, 3, -1, -2, -3];

function countPositiv(p, c, i, a)
{ 
  if(c &gt; 0){
    return p+1; 
  } else {
    return p;
  }
}

var positiv = arr.reduce(countPositiv, 0);

console.log(positiv);
I don't think there is much to review, it looks ok. I would just do it inline, and there is no need to list arguments you are not using:

var positiv = arr.reduce(function(acc, x) {
  return x &gt; 0 ? acc + 1 : acc;
}, 0);