Write add data in JSON file using Node js

Question

I am trying to write JSON file using node from loop data  e g    let jsonFile   require  jsonfile     for  i   0  i  lt  11  i          jsonFile writeFile  loop json    id      i     square      i   i       outPut in loop json is   id  1 square   1   but I want output file like this  below  and also if I run that code again it should add that new output as elements in same existing JSON file         table                      Id   1            square   1                            Id   2            square   3                            Id   3            square   9                            Id   4            square   16                            Id   5            square   25                            Id   6            square   36                            Id   7            square   49                            Id   8            square   64                            Id   9            square   81                            Id   10            square   100                  I want to use same file that I created 1st time but whenever I run that code new elements should add in that same file  const fs   require  fs     let obj         table         fs exists  myjsonfile json   function exists         if  exists             console log  yes file exists             fs readFile  myjsonfile json   function readFileCallback err  data                 if  err                    console log err                 else                   obj   JSON parse data                    for  i   0  i  lt  5  i                          obj table push                           id  i                          square  i   i                                                            let json   JSON stringify obj                   fs writeFile  myjsonfile json   json                                   else            console log  file not exists             for  i   0  i  lt  5  i                  obj table push                   id  i                  square  i   i                                    let json   JSON stringify obj           fs writeFile  myjsonfile json   json

User · Answer

you should read the file  every time you want to add a new property to the json  and then add the the new properties  var fs   require  fs    fs readFile  data json  function err content     if err  throw err    var parseJson   JSON parse content     for  i 0  i  lt 11   i        parseJson table push  id i  square i i         fs writeFile  data json  JSON stringify parseJson  function err       if err  throw err

User · Answer

For formatting jsonfile gives spaces option which you can pass as a parameter      jsonfile writeFile file  obj   spaces  2   function  err             console error err           Or use jsonfile spaces   4  Read details here   I would not suggest writing to file each time in the loop  instead construct the JSON object in the loop and write to file outside the loop   var jsonfile   require  jsonfile    var obj         table             for  i 0  i  lt 11   i            obj table push   id  i  square  i i      jsonfile writeFile  loop json   obj   spaces 2   function err         console log err

User · Answer

Please try the following program  You might be expecting this output   var fs   require  fs     var data      data table      for  i 0  i  lt 26   i        var obj            id  i         square  i   i         data table push obj    fs writeFile   input json   JSON stringify data   function err        if  err  throw err      console log  complete               Save this program in a javascript file  say  square js   Then run the program from command prompt using the command node square js  What it does is  simply overwriting the existing file with new set of data  every time you execute the command   Happy Coding

User · Answer

If this JSON file won t become too big over time  you should try   Create a JavaScript object with the table array in it var obj        table          Add some data to it  for example  obj table push  id  1  square 2      Convert it from an object to a string with JSON stringify var json   JSON stringify obj     Use fs to write the file to disk var fs   require  fs    fs writeFile  myjsonfile json   json   utf8   callback     If you want to append it  read the JSON file and convert it back to an object fs readFile  myjsonfile json    utf8   function readFileCallback err  data       if  err           console log err         else       obj   JSON parse data     now it an object     obj table push  id  2  square 3      add some data     json   JSON stringify obj     convert it back to json     fs writeFile  myjsonfile json   json   utf8   callback      write it back          This will work for data that is up to 100 MB effectively  Over this limit  you should use a database engine  UPDATE  Create a function which returns the current date  year month day  as a string  Create the file named this string    json  the fs module has a function which can check for file existence named fs stat path  callback   With this  you can check if the file exists  If it exists  use the read function if it s not  use the create function  Use the date string as the path cuz the file will be named as the today date    json  the callback will contain a stats object which will be null if the file does not exist

User · Answer

Above example is also correct  but i provide simple example   var fs   require  fs    var sampleObject         name   pankaj       member   stack       type            x  11          y  22           fs writeFile    object json   JSON stringify sampleObject  null  4    err    gt        if  err            console error err           return             console log  File has been created

User · Answer

For synchronous approach  const fs   require  fs   fs writeFileSync  file json   JSON stringify jsonVariable

User · Answer

try  var fs   require  fs    var sampleObject     your data     fs writeFile    object json   JSON stringify sampleObject  null  4    err    gt        if  err     console error err    return         console log  File has been created

User · Answer

I agree with above answers  Here is a complete read and write sample for anyone who needs it       router post      function req  res  next             console log req body           var id   Math floor  Math random   100  1            var tital   req body title          var description   req body description          var mynotes     quot Id quot   id   quot Title quot  tital   quot Description quot   description                    fs readFile  db json   utf8   function err data               var obj   JSON parse data               obj push mynotes               var strNotes   JSON stringify obj               fs writeFile  db json  strNotes  function err                   if err  return console log err                   console log  Note added

[javascript] Write / add data in JSON file using Node.js

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