How to update a value in a json file and save it through node js

Question

How do I update a value in a json file and save it through node js  I have the file content   var file content   fs readFileSync filename   var content   JSON parse file content   var val1   content val1    Now I want to change the value of val1 and save it to the file

User · Answer

Doing this asynchronously is quite easy  It s particularly useful if you re concerned for blocking the thread  likely   const fs   require  fs    const fileName      file json   const file   require fileName        file key    quot new value quot        fs writeFile fileName  JSON stringify file   function writeJSON err      if  err  return console log err     console log JSON stringify file      console log  writing to     fileName        The caveat is that json is written to the file on one line and not prettified  ex       quot key quot    quot value quot     will be      quot key quot    quot value quot    To avoid this  simply add these two extra arguments to JSON stringify JSON stringify file  null  2   null - represents the replacer function   in this case we don t want to alter the process  2 - represents the spaces to indent

User · Answer

I would strongly recommend not to use synchronous  blocking  functions  as they hold other concurrent operations  Instead  use asynchronous fs promises  const fs   require  fs   promises  const setValue    fn  value    gt     fs readFile fn       then body   gt  JSON parse body        then json   gt             manipulate your data here       json value   value       return json             then json   gt  JSON stringify json        then body   gt  fs writeFile fn  body        catch error   gt  console warn error    Remeber that setValue returns a pending promise  you ll need to use  then function or  within async functions  the await operator     await operator await setValue  temp json   1               save  quot value quot   1 await setValue  temp json   2               then  quot value quot   2 await setValue  temp json   3               then  quot value quot   3     then-sequence setValue  temp json   1                     save  quot value quot   1    then      gt  setValue  temp json   2       then save  quot value quot   2    then      gt  setValue  temp json   3       then save  quot value quot   3

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addition to the previous answer add file path directory for the write operation   fs writeFile path join   dirname jsonPath   JSON stringify newFileData   function  err

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For those looking to add an item to a json collection function save item  path      collection json        if   fs existsSync path             fs writeFile path  JSON stringify  item           else           var data   fs readFileSync path   utf8              var list    data length    JSON parse data               if  list instanceof Array  list push item          else list    item            fs writeFileSync path  JSON stringify list

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read file and make object let content   JSON parse fs readFileSync  file json    utf8        edit or add property content expiry date   999999999999    write file fs writeFileSync  file json   JSON stringify content

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change the value in the in-memory object content val1   42    Serialize as JSON and Write it to a file fs writeFileSync filename  JSON stringify content

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Save data after task completion fs readFile  quot   sample json quot    utf8   function readFileCallback err  data            if  err              console log err             else             fs writeFile  quot   sample json quot   JSON stringify result    utf8   err   gt                if  err  throw err              console log  File has been saved

[json] How to update a value in a json file and save it through node.js

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