Set implementation in JavaScript

gistfile1.txt

var ISet = function(array) {
  this.list = array ? toSet(array) : [];
};

ISet.prototype.add = function(inValue) {
  if (exists(this.list, inValue) < 0) {
    this.list.push(inValue);
    return true;
  }
  return false;
};

ISet.prototype.remove = function(item) {
  var idx = exists(this.list, item);
  if (idx > 0) {
    this.list.splice(idx, 1);
  }
  return idx > 0;
};

ISet.prototype.getValues = function() {
  return this.list;
}

ISet.prototype.toSet = function(array) {
  return toSet(array);
}

function toSet(array) {
  var copy = [].concat(array);
  for (var i = 0; i < copy.length; i++) {
    for (var j = i + 1; j < copy.length; j++) {
      if (copy[i] === copy[j]) {
        copy.splice(j--, 1);
      }
    }
  }
  return copy;
}

ISet.prototype.size = function() {
  return this.list.length;
};

ISet.prototype.clear = function() {
  this.list = [];
};

function exists(list, item) {
  for (var i = 0; i < list.length; i++) {
    if (list[i] === item) {
      return i;
    }
  }
  return -1;
}