How to try catch statements that return promise objects in JS

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Preface

You must study technology deeply when you are idle , Life is meaningful , Know what it is and don't know why it is , It's terrible , It is doomed that technology will not go far

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One 、 What is the Promise？

To understand this thing , Look directly at the official documents , Portal

Two 、 Code demonstration try catch

1. nothing async Modifier , nothing new Promise

function tryError () {
    
  try {
    
    console.log(a)
  } catch (e) {
    
    console.log(e)
  }
}

For the above synchronization code , Well understood. , Errors can be captured normally

2. Yes async Modifier , nothing new Promise

async function tryError () {
    
  try {
    
    console.log(a)
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Function added async Modifier , Errors can also be captured normally , The difference is that after executing the function , At the same time, a Promise object , Give it a try , Get Promise After the object can catch abnormal

async function tryError () {
    
  console.log(a)
}
tryError()

After console verification , No problem , Abnormally successful catch 了

3. nothing async Modifier , Yes new Promise,Promise No inside async

function tryError () {
    
  try {
    
    return new Promise((resolve, reject) => {
    
      throw new Error('error')
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Find out in this case , It's impossible catch Anomalous , Well, if it's in new Promise after catch Well ？ Give it a try ,

function tryError () {
    
  try {
    
    return new Promise((resolve, reject) => {
    
      throw new Error('error')
    }).then(res => {
    
      console.log(res)
    }).catch(e => {
    
      console.log('catch：' + e)
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Results found , stay .catch The exception was successfully caught

4. nothing async Modifier , Yes new Promise,Promise There are async

function tryError () {
    
  try {
    
    return new Promise(async (resolve, reject) => {
    
      throw new Error('error')
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Find out in this case , It's impossible catch Anomalous , Well, if it's in new Promise after catch Well ？ Give it a try ,

function tryError () {
    
  try {
    
    return new Promise(async (resolve, reject) => {
    
      throw new Error('error')
    }).then(res => {
    
      console.log(res)
    }).catch(e => {
    
      console.log('catch：' + e)
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Results found , stay .catch It still cannot catch exceptions

5. Yes async Modifier , Yes new Promise,Promise No inside async

async function tryError () {
    
  try {
    
    return new Promise((resolve, reject) => {
    
      throw new Error('error')
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Find out in this case , It's impossible catch Anomalous , Well, if it's in new Promise after catch Well ？ Give it a try ,

async function tryError () {
    
  try {
    
    return new Promise((resolve, reject) => {
    
      throw new Error('error')
    }).then(res => {
    
      console.log(res)
    }).catch(e => {
    
      console.log('catch：' + e)
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Results found , stay .catch The exception was successfully caught

6. Yes async Modifier , Yes new Promise,Promise There are async

async function tryError () {
    
  try {
    
    return new Promise(async (resolve, reject) => {
    
      throw new Error('error')
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Find out in this case , It's impossible catch Anomalous , Well, if it's in new Promise after catch Well ？ Give it a try ,

async function tryError () {
    
  try {
    
    return new Promise(async (resolve, reject) => {
    
      throw new Error('error')
    }).then(res => {
    
      console.log(res)
    }).catch(e => {
    
      console.log('catch：' + e)
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Results found , stay .catch It is still unable to capture

7. Yes async Modifier , Yes await new Promise,Promise No inside async

async function tryError () {
    
  try {
    
    return await new Promise((resolve, reject) => {
    
      throw new Error('error')
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

In this case , Find success catch It's abnormal , Well, if it's in new Promise after catch Well ？ Give it a try ,

async function tryError () {
    
  try {
    
    return await new Promise((resolve, reject) => {
    
      throw new Error('error')
    }).then(res => {
    
      console.log(res)
    }).catch(e => {
    
      console.log('catch：' + e)
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Results found , stay .catch The exception was successfully caught

8. Yes async Modifier , Yes await new Promise,Promise There are async

async function tryError () {
    
  try {
    
    return await new Promise(async (resolve, reject) => {
    
      throw new Error('error')
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

In this case , Find that you can't catch abnormal , Well, if it's in await new Promise after catch Well ？ Give it a try ,

async function tryError () {
    
  try {
    
    return await new Promise(async (resolve, reject) => {
    
      throw new Error('error')
    }).then(res => {
    
      console.log(res)
    }).catch(e => {
    
      console.log('catch：' + e)
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Results found , stay .catch It still cannot catch exceptions

3、 ... and 、 The illustration try catch

so Promise The correct usage of error capture in is ：
stay async Function internal use try catch Catch asynchronous errors
promise For internal use .catch Method to capture promise Internal code error

Four 、 Immediate execution function

function tryError () {
    
  try {
    
    (async () => {
    
      throw new Error('error')
    })()
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

It can be seen that the immediate execution function is as long as you bring async Modifier , It's impossible catch Anomalous , Except in async Then use .catch To capture ,

function tryError () {
    
  try {
    
    (async () => {
    
      throw new Error('error')
    })().catch(e => {
    
      console.log('catch：' + e)
    })
  } catch (e) {
    
    console.log(e)
  }
}
tryError()

Results found , stay .catch The exception was successfully caught

5、 ... and 、 Abnormal no catch, The code will not continue to execute

Be careful ： Abnormal no catch, The code will not continue to execute

6、 ... and 、 Reference documents

JS Medium async/await The usage and understanding of
Use Promise
promise Error capture in