Question

¿在nodeJS中使用.catch((err)=>{})实现承诺错误处理程序async/await的最佳做法是什么？

代码在 nodeJS V8.10.0 中运行

以下是我实施后者的失败尝试。

请考虑以下代码：

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);
})

CONSOLE OUTPUT：

控制台输出表示未处理的承诺拒绝。

非常欢迎任何指向正确方向的指针，以及反模式中的更正或代码中的错误做法。

提前感谢您的时间和兴趣。

解决

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

查看您的代码，不确定您要执行的操作。如果它创建两个承诺，然后随机拒绝或解决，。

以下是您修改后的代码 - ＆gt;

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);
})

Answer 2

在第二个示例中，您应抛出异常而不是尝试拒绝承诺。

async function asyncFnc2(){
    try{
          var res1 = await promise1;
          var res2 = await promise2;
          return res1 + ' ' +res2;
    }catch(e){
        throw new Error(e);
    }
}

如何使用async / await处理错误？

2 个答案: