equals method is missing

[valioDOTch]

I would suggest the following equals method

equals: function equals(otherSet){
    //if (!otherSet instanceof Set){return false;} //comment out for typecheck
    var otherKeys = Object.keys(otherSet._values).sort();
    var myKeys = Object.keys(this._values).sort();
    return JSON.stringify(otherKeys) === JSON.stringify(myKeys);
}

[lukasolson]

If you would like to open a pull request with this, I'd be open to reviewing/merging it.

The only difference I would suggest is, instead of using JSON.stringify, use this._hashFunction, which defaults to JSON.stringify.