Google App Script - Export google sheet to JSON file and save it on google drive.

exporter.js

/**
 * onOpen adds Export JSON option in spreadsheet tool bar
 * exportJSON prepares json from sheet, save it in same folder as of spreadsheet on google drive and display it in modal with download link
 * turn on Drive API on script editor, Resources -> Advanced Google Services -> Drive API
 */

function onOpen() {
  var sheet = SpreadsheetApp.getActiveSpreadsheet();
  var entries = [{
    name : "Run",
    functionName : "exportJSON"
  }];
  sheet.addMenu("Export JSON", entries);
};

// triggers parsing and displays results in a text area inside a custom modal window
function exportJSON() {
  var activeSpreadsheet = SpreadsheetApp.getActiveSpreadsheet()
  var activeSheet = SpreadsheetApp.getActiveSheet();
  var jsonData = JSON.stringify( makeJson(activeSheet.getDataRange().getValues()),null, 4)
  var sheetDrivefile = DriveApp.getFileById(activeSpreadsheet.getId());
  var folders = sheetDrivefile.getParents().next().getId();
  var d = new Date();
  var n = d.getTime(); // add timestamp in file title
  
  // https://github.com/googleapis/google-api-nodejs-client/issues/96
  var fileSets = {
    title: 'your_json_file_name' + n + '.json',
    mimeType: 'application/json',
    parents: [{id: folders}]
  };

  var blob = Utilities.newBlob(jsonData, "application/vnd.google-apps.script+json");
  var file = Drive.Files.insert(fileSets, blob);
  var output = HtmlService.createHtmlOutput('<title> JSON export results - select all and copy!</title><a download="your_file_name_here'+n+'.json" target="_blank" href="'+ file.webContentLink +'">Download from here</a><pre class="prettyprint">' + jsonData + '</pre>');
  SpreadsheetApp.getActiveSpreadsheet().show(output);
};

function makeJson(data) {
  var obj = {};
  var result = [];
  var headers = data[0];
  var cols = headers.length;
  var row = [];

  for (var i = 1, l = data.length; i < l; i++)
  {
    // get a row to fill the object
    row = data[i];
    // clear object
    obj = {};
    for (var col = 0; col < cols; col++) 
    {
      // fill object with new values
      obj[headers[col]] = row[col];    
    }
    // add object in a final result
    result.push(obj);  
  }
  // console.log(result)
  return result;  
  
    
    
}