CODEWITHSUNDEEP
javascriptnode.jsasync-awaitnode-async
bazaars
bazaars

Reputation: 488

node async library filterLimit always returns undefined

I'm trying to async filter a list of file paths to return only existing files. I'm using the async library's filterLimit along with fs-extra. Function below:

const asyncFilter = require('async').filterLimit;
const fsExtra = require('fs-extra');

async function filterFiles(fileList){
  const existing = await asyncFilter(fileList, 5, (file, callback) => {
    console.log(file); // looks good

    fsExtra.pathExists(file, (err, exists) => {
       const result = err ? false : exists;
       console.log(result); // looks good (boolean)

       callback(null, result);
    });
  });

  console.log(existing); // always undefined...
}

Upvotes: 1

Views: 167

Answers (1)

exside
exside

Reputation: 3894

EDIT 2: Both suggestions below do not work... here is a working version where the deprecated fs.exists() was replaced with fs.access()

const async = require('async');
const fs = require('fs');

async function filterFiles(fileList) {
    try {

        const result = await async.filterLimit(fileList, 5, function(filePath, callback) {
            fs.access(filePath, function(err) {
                callback(null, !err)
            });
        });

        console.log(result);
    } catch(err) {
        console.log(err);
    }
};

Can't you simply do:

NOT WORKING

    const asyncFilter = require('async').filterLimit;
    const fs = require('fs');

    async function filterFiles(fileList) {
        let result = [];
        await asyncFilter(fileList, 5, fs.exists, function(existing) {
            // array of existing files
            console.log(existing);
            // now assign the existing files to result array
            result = existing;
        });
        // should be the same as existing in callback function
        console.log(result);
    };

no need for fs-extra. I think your issue is that async.filterLimit() does not return anything but executes a callback function, so just by assigning async.filterLimit() to a variable does not mean you get the result in there, you'll get undefined because the function does not return anything!

EDIT: Adapted snippet from above based on @Jaromanda X's comment:

    const asyncFilter = require('async').filterLimit;
    const fs = require('fs');

    async function filterFiles(fileList) {
        let result = await asyncFilter(fileList, 5, fs.exists);
        // should contain only existing files
        console.log(result);
    };

Upvotes: 1

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