HashSet implementation in Javascript

<script>
function HashSet() {
    this._arr = new Array();
}

HashSet.prototype.add = function(e) {
    var arr = this._arr;
    var i = arr.indexOf(e);
    if (i == -1) arr.push(e);
}

HashSet.prototype.get = function(i) {
    return this._arr[i];
}

HashSet.prototype.size = function(i) {
    return this._arr.length;
}

HashSet.prototype.remove = function(e) {
    var arr =this._arr;
    var i = arr.indexOf(e);
    if (i != -1) arr.splice(i, 1);
}

HashSet.prototype.toString = function() {
    return this._arr.join(',');
}

/*
var startTime = new Date();
var set = new HashSet();
for(i = 0; i < 10004; i++) { //it took 3 seconds to do; with 100000 elements, my browser hangs
    set.add('Index ' + i); // value also effect to time complete task
}
set.add('One');
set.add('Two');
set.add('Three');
set.add('Four');
set.add('Five');

set.add('One');//will be ignored
set.add('One');//will be ignored

set.remove('Five');
var finishTime = new Date();
document.write(startTime + '<hr />' + set.size()  + ' distinct eles<hr />' + finishTime);
document.close();
*/


var a = [1, 2, 3, 4, 5];

function MyIntSet(n) {
    this.N = n;
    this._partitions = new Array();
    var i;
    for (i = 0; i < n; i++) {
        this._partitions[i] = new HashSet();
    }
}

MyIntSet.prototype.add = function(e) {
    // e Object - y = f(e) - y Int
    // assume that e is alreay Int
    var iP = e % this.N;
   
    var set = this._partitions[iP];
    set.add(e);
}

MyIntSet.prototype.get = function(i) {
    return -1;
}

MyIntSet.prototype.size = function(i) {
    var r = 0;
    for (i = 0; i < this.N; i++) {
        r += this._partitions[i].size();
    }
    return r;
}

MyIntSet.prototype.remove = function(e) {
    var iP = e % this.N;
   
    var set = this._partitions[iP];
    set.remove(e);
}

MyIntSet.prototype.toString = function() {
    var r = '';
    for (i = 0; i < this.N; i++) {
        var pi = this._partitions[i].toString();
        if (pi != '') r = r + pi + ',';
    }
    if (r != '') r = r.substring(0, r.length - 1);
    return r;
}


var startTime = new Date();
var xset = new MyIntSet(5000);
for(i = 0; i < 1000000; i++) {
    xset.add(i);
    xset.add(i); // will be ignored
}
document.write(startTime + '<hr />' + xset.size() + ' elements<hr />' +  new Date());
document.close();


/*
var arr = new Array();
for (i = 0; i < 5000000; i++) {
    arr.push(i);
}
document.write(startTime + '<hr />' + arr.length + ' elements<hr />' +  new Date());
document.close();
*/
</script>