Cannot handle an error inside a promise

I have this function that takes a path and fetches some information about it (using node.js capabilities)

import fs from 'fs'
import fse from 'fs-extra'
import { join } from 'path'


/**
* Take in file path and return contents with stat
* @param {String} path
* @return {Array}
*/
export default path => {
return readdir(path).then(files => {
const statsPromises = files.map((file, i) => {
const p = join(path, file)
return stat(p).then(stat =>
({
// THIS ONE LINE BELOW THROWS UN-HANDLED ERRORS FOR SOME PATHS
// Error: EPERM: operation not permitted, scandir
folderItemsCount: stat.isDirectory() ? fs.readdirSync(p).length : null,
name: file,
path: p,
stat
})
, err => console.log("Path access error ", err))
})
return Promise.all(statsPromises)
}).then(contents =>
contents.filter(Boolean)
)
}


// ============== HELPER FUNCTIONS ==============
/**
* Get Array for path contents. Checks if path exists
* @param {String} path
* @return {Promise}
*/
export function readdir (path) {
return pathExists(path)
? fse.readdir(path)
: Promise.reject(new Error('Path does not exist'))
}

/**
* Alias of fse.existsSync
* @param {String} path
* @return {Boolean}
*/
export function pathExists (path) {
return fse.existsSync(path)
}

/**
* Get path stat
* @param {String} path
* @return {Promise}
*/
export function stat (path) {
return fse.stat(path)
}


I don't know how to handle the error for the following line:

folderItemsCount: stat.isDirectory() ? fs.readdirSync(p).length : null


I want it to:

return a number of items if it can access a folder (this does work when it checks accessible dirs)

return a string "unknown" (or null) if it cannot access a folder instead of throwing an un-handled error: Error: EPERM: operation not permitted, scandir

Error: EPERM: operation not permitted, scandir

The line below handles stat() but not scandir()

stat()

scandir()

, err => console.log("Path access error ", err))


2 Answers
2

Without digging too much into your code, a promise either resolves or rejects, which your handlers either hit the 'then' or the 'catch'. I see you're using .then, but not .catch. Also keep in mind that Promise.all will reject if any promise in that list rejects, so you've got an all-or-nothing promise there.

folderItemsCount:

stat()

, err => console.log("Path access error ", err))

folderItemsCount:

scandir()

I solved the problem by adding a try/catch

try/catch

export default path => {
return readdir(path).then(files => {
const statsPromises = files.map((file, i) => {
const p = join(path, file)
return stat(p).then(stat =>
let countResult
if (stat.isDirectory()) {
try {
countResult = fs.readdirSync(p).length
}
catch (error) {
countResult = 'unknown'
}
} else { countResult = null }
return ({
folderItemsCount: countResult,
name: file,
path: p,
stat
})
, err => console.log("Path access error ", err))
})
return Promise.all(statsPromises)
}).then(contents =>
contents.filter(Boolean)
)
}


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