Cannot read property 'map' of undefined Node js

Question

I am getting the Error, I am writing a function to monitor a path for. I am new to Node.js:

TypeError: Cannot read property 'map' of undefined

at C:\Users\a\Desktop\DL\file\filemonitor.js:15:14 at FSReqWrap.oncomplete (fs.js:149:20)

const Promise = require ('bluebird');
var fs = Promise.promisifyAll(require("fs"));

monitordir(monitorpath) {
  var fileList = [];
  return new Promise((resolve, reject) => {
    fs.readdir(monitorpath,function(err, items) {
      items.map((file) => {
        fileList.push(file);
      });
      resolve(fileList);
    });
  })
}

Note: I don't see a package.json file either. Should I have a sucessful run to see it

So, what would ypu suggest i need to do to rectify it. I was told that Promise.promisifyAll you add a suffix Aysnc and hence i added a function to readdir — alangilbi
– alangilbi, Commented Apr 12, 2018 at 19:49

Nicolas Takashi · Accepted Answer · 2018-04-12 20:16:50Z

1

When you run var fs = Promise.promisifyAll(require("fs")); it return a promise to you. So you can't execute a map of a promise.

I believe that you don't need a Promise to resolve fs module, my suggestion is you write something like that.

const Promise = require('bluebird');
const fs = require("fs");

const monitordir = path => {
    return new Promise((resolve, reject) => {
        fs.readdir(path, (error, items) => {
            if (error) return reject(error)
            return resolve(items);
        })
    })
}

answered Apr 12, 2018 at 20:16

Nicolas Takashi

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2 Comments

alangilbi Over a year ago

So i change my code to this and i still get the same error const Promise = require('bluebird'); //var fs = Promise.promisifyAll(require("fs")); var fs = require('fs'); monitorDir(monitorPath) { var fileList = []; return new Promise((resolve, reject) => { fs.readdir(monitorPath, function(err, items) { items.map((file) =>{ fileList.push(file); }); resolve(fileList); }); }) }

Nicolas Takashi Over a year ago

Hey buddy! I created a gist to show you how I implemented the code above. gist.github.com/nicolastakashi/7cb5cbea674a586f644ee561e96d3ac6 I hope this helps

Zeeshan Hassan Memon · Accepted Answer · 2018-04-12 20:11:10Z

0

Try following fix, see if it fits your needs:

monitordir(monitorpath)
{
    var fileList = [];
    return fs.readdir(monitorpath)
        .then(function(err,items) {
            items.map((file) => {
                fileList.push(file); // fileList is ready here! do whatever you want before it resolves to caller
            });
            return fileList;
        })
        .catch(function(e) {
            // something bad happened; throw error or handle it as per your needs
            throw new Error(e);
        });
}

For package.json you can run npm init command at your project directory it will create one for you.

answered Apr 12, 2018 at 20:11

Zeeshan Hassan Memon

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3 Comments

alangilbi Over a year ago

Found out the answer, the monitor path was not setup right

Zeeshan Hassan Memon Over a year ago

great, but still I would suggest you to try to drop additional return new Promise((resolve,reject) => { since you have promisified the fs module, it will look cleaner and better without extra code needed.

alangilbi Over a year ago

Thanks Zeeshan, will do that

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