let obj = {"zzz": "ZZZZ", "aa": "AAAA", "title": "TITLE"} if (obj["bb"] == undefined) { console.log("bb is undefinded") } else { console.log("bb is not undefinded") } //这边bb已经声明，所以可以直接与undefined对比判断 let bb = obj["bb"] if (bb == undefined) { console.log("bb2 is undefinded") } else { console.log("bb2 is not undefinded") } //这边的cc未声明，无法确定cc是否之前已经声明，无法直接用==undefined对比判断，需要通过判断类型才能确定cc是否已经声明。 // cc的类型值 console.log("cc is:", typeof cc) // cc的类型值的类型 console.log("cc is:", typeof typeof cc) if (typeof cc == "undefined") { console.log("cc is undefinded") } else { console.log("cc is not undefinded") } //取得对象的第一个属性值 console.log("对象的第一个属性值：", fnObject_current(obj)) console.log("对象是否为空：", fnObject_isNotNull(obj)); console.log("对象是否为空：", fnObject_isNotNull(obj["dd"]));