Javascript中的集合

集合是由一组无序且唯一（即不能重复）的项组成

function Set() {
        var items={};
        this.has=function(value){
          //return value in items;
          return this.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(){
          return Object.keys(items).length;
        }
        this.sizeLegacy=function(){
          var count=0;
          for (var prop in items) {
            if (items.hasOwnProperty(prop)) {
              ++count;
            }
          }
        }
        this.values=function () {
          return Object.keys(items);
        }
        this.valuesLagacy=function () {
          var keys=[];
          for (var key in items) {
            if (items.hasOwnProperty(key)) {
                keys.push(key);
            }
          }
          return keys;
        }
        //并集
        this.union=function(otherSet) {
          var unionSet=new Set();
          var values=this.values();
          for (var i = 0; i < values.length; i++) {
            unionSet.add(values[i]);
          }
          values=otherSet.values();
          for (var i = 0 i < values.length; i++) {
            unionSet.add(values[i]);   
          }
          return unionSet;
        }
        // 交集
        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;
        }
        // 差集
        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;
        }
        // 子集
        this.isSubsetOf=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;
          }
        }
}