function  Set() {    var items = {};    this.has = function(value){        return items.hasOwnProperty(value);    };    this.add = function(value){        if (!this.has(value)){            items[value] = value;            return true;        }        return false;    };    this.remove = function(value){        if (this.has(value)) {            delete items[value];            return true;        }        return false;    };    this.clear = function(){        items = {};    };    this.size = function(){        var count = 0;        for (var prop in items){            if(items.hasOwnProperty(prop)){                ++count;            }        }        return count;    };    this.values = function(){        var keys = [];        for (var key in items){            keys.push(key);        }        return keys;    };    this.union = function(otherSet){        var unionSet = new Set();        var values = this.values();        for(var i=0; i<values.length; i++){            unionSet.add(values[i]);        }        var values = otherSet.values();        for(var i=0; i<values.length; i++){            unionSet.add(values[i]);        }        return unionSet;    };    this.intersection = function(otherSet){        var intersectionSet = new Set();        var values = this.values();        for(var i=0; i<values.length; i++){            if (otherSet.has(values[i])){                intersectionSet.add(values[i]);            }        }        return intersectionSet;    };    this.difference = function(otherSet){        var differenceSet = new Set();        var values = this.values();        for(var i=0; i<values.length; i++){            if(!otherSet.has(values[i])){                differenceSet.add(values[i]);            }        }        return differenceSet;    };    this.subset = function(otherSet){        if (this.size() > otherSet.size()){            return false;        } else {            var values = this.values();            for(var i=0; i<values.length; i++){                if(!otherSet.has(values[i])){                    return false;                }            }            return true;        }    }}var set = new Set();set.add(1);console.log(set.values()); //输出["1"]console.log(set.has(1)); //输出trueconsole.log(set.size()); //输出1set.add(2);console.log(set.values()); //输出["1", "2"]console.log(set.has(2)); //trueconsole.log(set.size()); //2set.remove(1);console.log(set.values()); //输出["2"]set.remove(2);console.log(set.values()); //输出[]var setA = new Set();setA.add(1);setA.add(2);setA.add(3);var setB = new Set();setB.add(3);setB.add(4);setB.add(5);setB.add(6);var unionAB = setA.union(setB);console.log(unionAB.values());var setA = new Set();setA.add(1);setA.add(2);setA.add(3);var setB = new Set();setB.add(2);setB.add(3);setB.add(4);var intersectionAB = setA.intersection(setB);console.log(intersectionAB.values());var setA = new Set();setA.add(1);setA.add(2);setA.add(3);var setB = new Set();setB.add(2);setB.add(3);setB.add(4);var differenceAB = setA.difference(setB);console.log(differenceAB.values());var setA = new Set();setA.add(1);setA.add(2);var setB = new Set();setB.add(1);setB.add(2);setB.add(3);var setC = new Set();setC.add(2);setC.add(3);setC.add(4);console.log(setA.subset(setB));console.log(setA.subset(setC));