node内存管理

简单缓存

let LimitableMap=function (limit) {  this.limit=limit || 10;  this.map={};  this.keys=[];};let hasOwnProperty=Object.prototype.hasOwnProperty;LimitableMap.prototype.set=function (key,value) {  let map=this.map;  let keys=this.keys;  if (!hasOwnProperty.call(map,key)) {      if (keys.length===this.limit) {          let firstKey=keys.shift();          delete map[firstKey];      }      keys.push(key);  }  map[key]=value;};LimitableMap.prototype.get=function (key) {  return this.map[key];};module.exports=LimitableMap;