赋值
let obj = {x:undefined, y:null}
判断是否为 undefined 或 null
let obj = {x:undefined, y:null}
obj.x === undefined; //true
obj.y === null; //true
obj.x === null; //false
obj.y === undefined; //false
区别
null是特殊的对象
undefined就是undefined
let obj = {x:undefined, y:null}
typeof(obj.x); // 'undefined'
typeof(obj.y); // 'object'
obj.x+1 // NaN
obj.y+1 // 1
