fs writeFile in a promise asynchronous-synchronous stuff

Question

I need some help with my code  I m new at Node js and have a lot of trouble with it   What I m trying to do   1  Fetch a  txt with Amazon products  ASINs     2  Fetch all products using the amazon-product-api package   3  Save each product in a  json file   My code is not working  I think I messed up with this asynchronous-synchronous stuff - help me   var amazon   require  amazon-product-api    var fs   require  fs     var client   amazon createClient       awsId   XXX       awsSecret   XXX       awsTag   888       var array   fs readFileSync    test txt   toString   split   n    for  var i   1  i  lt  array length  i           var ASIN   array i        return client itemLookup               domain   webservices amazon de               responseGroup   Large               idType   ASIN               itemId  ASIN                     then function results                fs writeFile ASIN     json   JSON stringify results   function err                    if  err                        console log err                     else                       console log  JSON saved                                                  return results              catch function err                console log err

User · Answer

If you want to import the promise based version of fs as an ES module you can do:

import { promises as fs } from 'fs'

await fs.writeFile(...)

As soon as node v14 is released (see this PR), you can also use

import { writeFile } from 'fs/promises'

User · Answer

Because fs writefile is a traditional asynchronous callback - you need to follow the promise spec and return a new promise wrapping it with a resolve and rejection handler like so   return new Promise function resolve  reject        fs writeFile   lt filename type gt    data    lt file-encoding gt    function err            if  err  reject err           else resolve data                 So in your code you would use it like so right after your call to  then       then function results        return new Promise function resolve  reject                fs writeFile ASIN     json   JSON stringify results   function err                   if  err  reject err                  else resolve data                                then function results           console log  results here      results       catch function err           console log  error here      err

User · Answer

For easy to use asynchronous convert all callback to promise use some library like  bluebird             then function results                    fs writeFile ASIN     json   JSON stringify results   function err                        if  err                            console log err                         else                           console log  JSON saved                            return results                                                            catch function err                    console log err                     Try solution with promise  bluebird   var amazon   require  amazon-product-api    var fs   require  fs    var Promise   require  bluebird     var client   amazon createClient       awsId   XXX       awsSecret   XXX       awsTag   888        var array   fs readFileSync    test txt   toString   split   n    Promise map array  function  ASIN        client itemLookup           domain   webservices amazon de           responseGroup   Large           idType   ASIN           itemId  ASIN        then function results            fs writeFile ASIN     json   JSON stringify results   function err                if  err                    console log err                 else                   console log  JSON saved                    return results                                  catch function err            console log err

User · Answer

Use fs writeFileSync inside the try catch block as below    var fs   require  fs     try        const file   fs writeFileSync ASIN     json   JSON stringify results        console log  JSON saved         return results     catch  error       console log err

User · Answer

Update Sept 2017  fs-promise has been deprecated in favour of fs-extra     I haven t used it  but you could look into fs-promise  It s a node module that      Proxies all async fs methods exposing them as Promises A  compatible   promises  when  Q  etc   Passes all sync methods through as values

User · Answer

const util   require  util   const fs   require  fs     const fs writeFile   util promisify fs writeFile   fs writeFile  message txt    Hello Node js        catch  error    gt            console log error

User · Answer

Finally  the latest node js release v10 3 0 has natively supported fs promises   const fsPromises   require  fs   promises     or require  fs promises   in v10 0 0 fsPromises writeFile ASIN     json   JSON stringify results      then      gt        console log  JSON saved            catch er   gt        console log er           You can check the official documentation for more details  https   nodejs org api fs html fs fs promises api

User · Answer

As of 2019        the correct answer is to use async await with the native fs promises module included in node  Upgrade to Node js 10 or 11  already supported by major cloud providers  and do this   const fs   require  fs   promises      This must run inside a function marked  async   const file   await fs readFile  filename txt    utf8    await fs writeFile  filename txt    test      Do not use third-party packages and do not write your own wrappers  that s not necessary anymore   No longer experimental  Before Node 11 14 0  you would still get a warning that this feature is experimental  but it works just fine and it s the way to go in the future  Since 11 14 0  the feature is no longer experimental and is production-ready   What if I prefer import instead of require   It works  too - but only in Node js versions where this feature is not marked as experimental   import   promises as fs   from  fs     async      gt        await fs writeFile    test txt    test    utf8

User · Answer

say  const util   require  util   const fs writeFile   util promisify fs writeFile    https   nodejs org api util html util util promisify original  this is less prone to bugs than the top-voted answer

User · Answer

What worked for me was fs promises  Example One  const fs   require  quot fs quot    fs promises    writeFile   dirname     test json    quot data quot     encoding   utf8        then      gt           Do whatever you want to do      console log  Done           Example Two  Using Async-Await  const fs   require  quot fs quot    async function writeToFile       await fs promises writeFile   dirname     test-22 json    quot data quot         encoding   utf8           console log  quot done quot      writeToFile

[node.js] fs.writeFile in a promise, asynchronous-synchronous stuff

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