在Sequencial异步函数中尝试/捕获错误

Question

I have a sequence of async functions that can be resolved or rejected. This functions must be executed in the correct sequence and depend one on other. So, i used 3 async functions and a try catch block. The problem is that when I reject some of the promises in the async functions, the catch block dont get the error sended on the reject callback. How can I get the error sended on reject? (code bellow)

Or should I use promise chaining? I would like to avoid this...

const methods = {

methodOne: async output => {

    return new Promise( (resolve, reject) => {

        if(error)
            reject(error) // want to get this error in try/catch block
        else 
            resolve()

        })

    })

},

methodTwo: async () => {

    return new Promise( (resolve, reject) => {

        if(error)
            reject(error)
        else 
            resolve('output')

        })

    })

},

methodThree: async () => {

    return new Promise( (resolve, reject) => {

        if(error)
            reject(error)
        else 
            resolve()

        })

    })

},

runMethods: async () => {

    return new Promise( async (resolve, reject) => {

        try {

            await methods.methodOne()
            const output = await methods.methodTwo()
            await methods.methodThree(output)
            resolve()


        } catch(error) {

            console.log(error)
            reject(error)

        }


    })


}

}

Answer 1

You don't need the try/catch . You should use the promise .catch when awaiting for the methods.

You also don't need to return new Promise (...) .

If your promise is rejected, it will go in the .catch of that promise, wich is different from regular catch .

You could just return nested promises.

runMethods: () => {    
    return methods.methodOne()
            .then(() => methods.methodTwo())
            .then(output  => methods.methodThree(output))                     
}

Answer 2

I usually come at it this way.

 const methods = { methodOne: () => { return new Promise((resolve, reject) => { setTimeout(() => { console.log('method1') resolve() },1000) }).catch(e=>console.log(e)) }, methodTwo: () => { return new Promise((resolve, reject) => { setTimeout(() => { console.log('method2') resolve() }, 1000) }).catch(e => console.log(e)) }, methodThree: () => { return new Promise((resolve, reject) => { setTimeout(() => { console.log('method3') reject('whoops something happened') }, 1000) }).catch(e => console.log(e)) }, runMethods: () => { let run = new Promise(resolve=>resolve(true)) run .then(result1 => methods.methodOne()) .then(result2 => methods.methodTwo()) .then(result3 => methods.methodThree()) .catch(e=>console.log(e)) } } methods.runMethods()