Add files parsed with async to an array in JavaScript

Question

I need to be able to loop through an array of file paths and filter out files that do not contain a particular string within them. The target array returns an empty array, but instead I want the target array to include the list of files that do not contain the string, with results parsed to remove a substring up to the last instance of the delimiter.

const fs = require('fs')

const fileList = ['/L1/L2/file1', '/L1/L2/file2', '/L1/L2/file3', '/L1/L2/file4']
const filterText = 'filter files that contain me'
let targetArray = []

async function parseIncompleteDocumentation() {
  try {
    const delimiter = '/'
    for (let componentFile of coveredComponentsDirectoryList)
      return new Promise((resolve, reject) => {
        fs.readFile(componentFile, 'utf8', function(err, content) {
          if (err) {
            reject(err)
          } else if (!content.includes(incompleteDocumentationFilter)) {
            resolve(
              existingIncompleteComponentDocumentationList.push(
                componentFile.substring(
                  componentFile.lastIndexOf(delimiter) + 1,
                  componentFile.length
                )
              )
            )
          }
        })
      }
    )
  } catch (err) {
    return console.log('error message', err) // eslint-disable-line no-console
  }
}

const finalArray = await parseFiles()
console.log(finalArray) // returns empty array

If file1 and file3 contain filterText, desired output would be ['file2', 'file4']

Promises and forEach don't mix. Try replacing with a simple for of. — Keith
– Keith, Commented Jul 23, 2020 at 15:51
@Keith I updated my question with your suggestion, but it's still printing an empty array. Any advice? — lane
– lane, Commented Jul 23, 2020 at 20:49

Charlie · Accepted Answer · 2020-07-23 16:04:48Z

1

There are few options:

Use async/await inside for...of loop.

for (let file of fileList) {

  await new Promise((resolve, reject) => {
      fs.readFile(file, 'utf8', (err, content) => {

         if (err)
           return reject(err);

         //....
         resolve()
      })
  })
}

Use readFileSync

fileList.forEach(file => {

   try{
      let content  = fs.readFileSync(file, 'utf8');
      //...
   }
   catch(e) {
      //....
   }
})

answered Jul 23, 2020 at 16:04

Charlie

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1 Comment

Keith Over a year ago

Option 2, of course could cause issues. Current versions of node also come with promisified versions of readFile etc to avoid the Promise constructor. nodejs.org/dist/latest-v10.x/docs/api/…

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