在这种情况下，为什么不尝试并抓住工作呢？

Question

I'm learning Node.js but cannot understand why this is not working. What is the problem? Thanks for an answer.

const fs = require('fs')
const path = require('path')

try {
    fs.mkdir(path.join(__dirname, '/test'), {}, err => {
    console.log(err)
    if (err) throw err
    })
}
catch (err) {
    console.log('file is already created')
}

This is the result:

Error: EEXIST: file already exists, mkdir 'c:\\Users\\stefa\\Desktop\\programming\\learning-node\\playground\\paths\\test'

Answer 1

Callback created by lambda expression of err => {/**/} is ran asynchronously. try-catch cannot catch that.

You should use Promise s/ Future s or synchronized version of fs.mkdir function, fs.mkdirSync .

Try something like this:

const fs = require('fs')
const path = require('path')

try {
    fs.mkdirSync(path.join(__dirname, '/test'));
}
catch (err) {
    console.log('file is already created')
}

or

const fs = require('fs');
const path = require('path');
const util = require('util');
const mkdirPromisifed = util.promisify(fs.mkdir);

(async() {
    // ... all other code also should be written in async manner ...
    try {
        await mkdirPromisifed(path.join(__dirname, '/test'));
    }
    catch (err) {
        console.log('file is already created')
    }
}());

Answer 2

As PsychoX said, the callback is called asynchronously .

You have a few choices:

1. Just use the callback

2. Use the promises-based fs API (or use util.promisify on mkdir , but...)

3. (Not recommended) Use the Sync versoin of mkdir ( mkdirSync )

Here's #1:

const fs = require('fs')
const path = require('path')

fs.mkdir(path.join(__dirname, '/test'), {}, err => {
    if (err) {
       console.log('file is already created')
       return
    }
    // Do the next thing here
})

Here's #2, using fsPromises.mkdir :

const fsp = require('fs').promises
const path = require('path')

fsp.mkdir(path.join(__dirname, '/test'))
.then(() => {
    // Do the next thing here
})
.catch(err => {
   console.log('file is already created')
})

or within an async function:

try {
    await fsp.mkdir(path.join(__dirname, '/test'))
    // Do the next thing here
} catch (err) {
   console.log('file is already created')
}