If you want the file to be valid JSON, you have to open your file, parse the JSON, append your new result to the array, transform it back into a string and save it again.

var fs = require('fs')

var currentSearchResult = 'example'

fs.readFile('results.json', function (err, data) {
    var json = JSON.parse(data)
    json.push('search result: ' + currentSearchResult)

    fs.writeFile("results.json", JSON.stringify(json))
})

If this JSON file won't become too big over time, you should try:

1. Create a JavaScript object with the table array in it

   var obj = {
      table: []
   };
   

2. Add some data to it, for example:

   obj.table.push({id: 1, square:2});
   

3. Convert it from an object to a string with JSON.stringify

   var json = JSON.stringify(obj);
   

4. Use fs to write the file to disk

   var fs = require('fs');
   fs.writeFile('myjsonfile.json', json, 'utf8', callback);
   

5. 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.

The proper way to handle this is to parse the JSON file, modify the object, and output it again.

var obj = require('file.json');
obj.newThing = 'thing!';
fs.writeFile('file.json', JSON.stringify(obj), function (err) {
  console.log(err);
});

The code you provided with the jsonfile library looks like a good start: you parse the json into an object, call .push(), and save something.

With raw Node calls (assuming the json file is a representation of an array):

var fs = require('fs');
function appendObject(obj){
  var configFile = fs.readFileSync('./config.json');
  var config = JSON.parse(configFile);
  config.push(obj);
  var configJSON = JSON.stringify(config);
  fs.writeFileSync('./config.json', configJSON);
}

appendObject({OnetimeCode : WEAS_Server_NewOneTimeCode});