Javascript Array two_sum()

Array.prototype.two_sum = function() {
  var answer = [];
  for(var i = 0; i < this.length; i++) {
    for(var j = i + 1 ; j < this.length; j++){
      if(this[i] + this[j] == 0){
        answer.push([i, j]);/* w ww  . j  a v  a 2  s.  com*/
      }
    }
  }
  return answer;
}

Array.prototype.two_sum = function(){
  var locations = [];

  this.forEach(function(element1, index1){
    this.forEach(function(element2, index2) {

      if (index2 > index1) {
        if ((element1 + element2) === 0) {
          locations.push([index1, index2]);
        }/*from   ww  w.  j  a v a 2  s .  c om*/
      }
    })
  }.bind(this))
  return locations;
}

var array = [-1, 0, 2, -2, 1];
console.log(array.two_sum())

Array.prototype.two_sum = function () {
  result = [];//from  ww w  .ja  va  2 s  .co  m

  for (var x = 0; x < this.length; x++) {
    for (var y = x + 1; y < this.length; y++) {
      if (this[x] + this[y] === 0)
        result.push([x, y]);
    }
  }

  return result;
};

Array.prototype.two_sum = function() {
  positions = [];// w w w.j av  a  2  s.  co m
  for(i=0; i<this.length-1; i++){
    for(j=i+1; j<this.length; j++){
      if (this[i] + this[j] === 0) {
        positions.push([i, j]);
      };
    }
  }
  return positions;
};

// a = [1, -1, 2, 3, 4, -3, 0, 0];
// console.log(a.two_sum());