JS如何判断一个对象是否为空、是否有某个属性

let obj1 = {}
let obj2 = {a:1}
function empty(obj){
  for (let key in obj){
    return false;    //非空
}
  return true;       //为空
}
console.log(empty(obj1)) //true为空
console.log(empty(obj2)) //false非空

let obj1 = {}
if(JSON.stringify(obj1) == "{}"){
   console.log("空对象")
}else {
   console.log("非空对象")
}

let obj1 = {}

if (Object.keys(obj1).length == 0){   
   console.log("空对象")
}else {
   console.log("非空对象")
}

if (obj2.a){
   console.log("对象有此属性")
}else {
   console.log("对象无此属性")
}

let obj2 = {a:1}
if ("a" in obj2){
   console.log("对象或其原型链上有此属性")
}else {
   console.log("对象或其原型链上无此属性")
}

let obj2 = {a:1}
if (obj2.hasOwnProperty("a")){
   console.log("对象上有此属性")
}else {
   console.log("对象上无此属性")
}