## 1.調用connect方法判斷判斷數據庫是否存在,之后調用方法,不用重新創建數據庫實例 ~~~ class DB{ static getInstance(){ if(!DB.instance){ DB.instance = new DB(); } return D.instance } constructor(){ // 數據庫是否連接 this.dbClient=""; this.connect(); } connect(){ if(!this.dbClient){ console.log("數據庫初次連接"); this.dbClient = "數據庫連接成功" } console.log("數據庫連接成功") return this.dbClient; } find(){ this.connect(); } } ~~~ ~~~ var cheng = new DB(); cheng.connect() var jiang = new DB(); ~~~ ## 2.單例模式 ~~~ var cheng = DB.getInstance(); cheng.connect() var jiang = DB.getInstance(); ~~~