1、？.使用
let res = obj?.data?.list
<=等价=>
let res = obj && obj.data && obj.data.list
2、？？使用
console.log(1 || "xx") //1
console.log(0 || "xx") //xx
console.log(null || "xx") //xx
console.log(undefined || "xx") //xx
console.log(-1 || "xx") //-1
console.log("" || "xx") //xx
console.log(1 ?? "xx") //1
console.log(0 ?? "xx") //0
console.log(null ?? "xx") //xx
console.log(undefined ?? "xx") //xx
console.log(-1 ?? "xx") //-1
console.log("" ?? "xx") //''
差异：忽0和空字符串等错误的值
