code: function findIndexInArray(array, callback) {
          var _length = array.length;
          for (var i = 0; i < _length; i++) {
              if (callback(array[i])) return i;
          }
          return -1;
      }
docs: Find position of an array element when callback function
  return true.
  
  @param array {array} Array to seek
  @param callback {function} Callback function to test element
  @returns {number} Index of eleement or -1 if not found