三种状态
1.pending：在过程中还没有后果
2.resolved：胜利
3.rejected：失败
状态变动
1、pending -> resolved
2、pending -> rejected
状态的体现
pending状态不会触发then和catch
resolved状态会触发后续的then回调函数
rejected状态会触发后续的catch回调函数
then和catch扭转状态
then失常状况下会返回resolved，报错则返回rejected
catch失常状况下会返回resolved，报错则返回rejected
测试题
//第一题（后果会打印进去1,3，返回resolved状态）Promise.resolve().then(()=>{ console.log(1) //1 resolved}).catch(()=>{ console.log(2)}).then(()=>{ console.log(3) // 3 resolved})//第二题(后果会打印进去1,2,3)Promise.resolve().then(()=>{ console.log(1) //1 throw new Error("error1") //rejected}).catch(()=>{ console.log(2) //2 resolved}).then(()=>{ console.log(3) //3 resolved})//第三题(后果会打印进去1,2)Promise.resolve.then(()=>{ console.log(1) //1 throw new Error("error1") //rejected}).catch(()=>{ console.log(2) //2 resolved}).catch(()=>{ console.log(3)})