function maxMinAvg(arr){
  var suma = 0;
  var newArray = [];
  var currentMax = arr[0];
  var currentMin = arr[0];

  /* PROMEDIO */

  for(var i = 0; i < arr.length; i++){
    suma = suma + arr[i];

  }

  var promedio = suma/arr.length;

  /* MAX */

  for(var i=0; i<arr.length; i++){
    if(arr[i] > currentMax){
      currentMax = arr[i];
    }
  }

  /* MIN */

  for(var i=0; i<arr.length; i++){
    if(arr[i] < currentMin){
      currentMin = arr[i];
    }
  }


  newArray.push(currentMax);
  newArray.push(currentMin);
  newArray.push(promedio);

  return newArray;

}

var array = [1,5,10,-2];

console.log(maxMinAvg(array));