StringSet class in JavaScript

StringSet.js

"use strict";

var StringSet = /* StringSet */ function() {
    this.set = {};

    this.add = /* bool */ function(/* String */ string) {
        var contains = this.contains(string);
        this.set[string] = true;
        return !contains;
    };

    this.remove = /* bool */ function(/* String */ string) {
        var contains = this.contains(string);
        delete this.set[string];
        return contains;
    };

    this.contains = /* bool */ function(/* String */ string) {
        return string in this.set;
    };
};