javascript - 如何使用 async/await 处理错误？

Question

¿使用 async/await 实现 Promise 错误处理程序 .catch((err)=>{}) 的最佳实践是什么在nodeJS中？

代码在nodeJS V8.10.0

中运行

这是我实现后者的不成功尝试。

考虑以下代码:

使用 .catch((err)=>{})

    //Function that rejects a promise with a probability of 50%
    function randomReject(resolve,reject){
        setTimeout(()=>{
          if(Math.random() > 0.5)
            resolve('Bigger than 1/2');
          else
            reject('Smaller than 1/2');
        },500)
     }

//Test promises
//THESE PROMISES ARE DECLARED INCORRECTLY
var promise1 = new Promise((resolve,reject)=>{ //HERE IS THE PROBLEM
    randomReject(resolve,reject);
})
var promise2 = new Promise((resolve,reject)=>{ //HERE IS THE PROBLEM
    randomReject(resolve,reject);
})
//EXPLANATION: Without a wrapper function around the promises, these will 
//run in place as soon as they are declared. And since there is no promise 
//rejection handler declared in the latter code these will cause an
//"UnhandledPromiseRejectionWarning" in NodeJS.

//Async function declaration
async function asyncFnc2(){
          var res1 = await promise1;
          var res2 = await promise2;
          return res1 + ' ' +res2; 
}

//Async function call
asyncFnc2().then((val)=>{
    console.log(val);
}).catch((err)=>{
    console.log(err);
})

控制台输出:

控制台输出指示未处理的 promise 拒绝。

非常欢迎任何正确方向的指针，以及代码中反模式或不良实践的更正。

预先感谢您的时间和兴趣。

解决方案

function randomReject(resolve,reject){
    setTimeout(()=>{
        if(Math.random() > 0.5)
            resolve('Bigger than 1/2');
        else
            reject('Smaller than 1/2');
    },500)
}

//Test promises
//These promises are wrapped around functions so they are not run in place
function promise1(){
        return new Promise((resolve,reject)=>{
             randomReject(resolve,reject);
        })
}
function promise2(){ 
        return new Promise((resolve,reject)=>{
             randomReject(resolve,reject);
        })
};
//These promises are wrapped around functions so they are not run in place

//No need for the "try catch", just let the async function do the dirty 
//work. 

async function asyncFnc2(){
          var res1 = await promise1();
          var res2 = await promise2();
          return res1 + ' ' +res2;
}

//Any exception will be automatically catch by the ".catch((err)=>{})"
asyncFnc2().then((val)=>{
    console.log(val);
}).catch((error)=>{
    console.log(error);
})

Answer 1

看着你的代码，不太确定你想做什么。如果它创建两个 Promise，然后随机拒绝或解决。

下面是您修改后的代码来执行此操作->

function randomReject(){
   return new Promise((resolve, reject) => {
       setTimeout(()=>{
        if(Math.random() > 0.5)
            resolve('Bigger than 1/2');
        else
            reject('Smaller than 1/2');
    },500)
   });
}

async function asyncFnc2(){
    var res1 = await randomReject();
    var res2 = await randomReject();
    return res1 + ' ' +res2;
}
asyncFnc2().then((val)=>{
    console.log(val);
}).catch((error)=>{
    console.log(error);
})