promise抛异常，执行队列

 //promise抛出异常
        new Promise((resolve,reject)=>{
            resolve("成功")
        }).then(res=>{
            if(res !== 200){
                // throw new Error("错误")
                // 或者
               return Promise.reject("异常")
            }
        }).catch(error=>{
            // console.log(error.message);
            console.log(error);
        })

promise的队列，按顺序执行：原理是需要等待上一个promise执行完才可以执行下一个

   //promise按顺序执行代码的封装
        /* 
        按顺序执行的话，就是等上一个primise执行完，再执行下一个
        */
        //1.这个是最基础的方式，代码比较冗杂
           let promise =Promise.resolve("薯片");
           promise.then(res =>{
              return new Promise(resolve=>{
                console.log(res);

                setTimeout(() => {
                resolve(res +"好吃")
               }, 1000);
              })
           }).then(res =>{
            return new Promise(resolve=>{
                console.log(res);
             setTimeout(() => {
                resolve(res +"不能多吃")
               }, 1000);
            })
           }).then(res=>{
               console.log(res);
           })

 2.该方式简化了  这里的promise的赋值就是相当于上一个promise执行完后，resolve()了，才执行下一个

      let promise = Promise.resolve("薯片");
        promise = promise.then(res => {
            return new Promise(resolve => {
                console.log(res);
                setTimeout(() => {
                    resolve(res + "好吃")
                }, 1000);
            })
        })
        promise = promise.then(res =>{
            return new Promise(resolve => {
                console.log(res);
                setTimeout(() => {
                    resolve(res +"不能多吃")
                }, 1000);
            })
        })
        promise.then(res =>{
            return new Promise(resolve => {
                console.log(res);

            })
        })

 3.最佳方式
        function query(nums) {
            let promise = Promise.resolve();
            nums.forEach(item => {
                promise = promise.then(() => {
                    return new Promise(resolve => {
                        setTimeout(() => {
                            console.log(item);
                            resolve()
                        }, 1000);
                    })
                })
            });
        }
        query([1, 2, 3, 4, 5, 6])

//结果都是一秒一秒按顺序执行

 function query(nums) {
            let promise = Promise.resolve();
            nums.forEach(item => {
                promise = promise.then(() => {
                    return item();
                })
            });
        }
        function p1() {
            return new Promise(resolve => {
                setTimeout(() => {
                    console.log("p1");
                    resolve()
                }, 1000);
            })
        }
        function p2() {
            return new Promise(resolve => {
                setTimeout(() => {
                    console.log("p2");
                    resolve()
                }, 1000);
            })
        }
        query([p1, p2])