The below should work for you.

All credit to Convert CSV to JSON in JavaScript (archived), by iwek:

//var csv is the CSV file with headers
function csvJSON(csv){
 
  var lines=csv.split("\n");
 
  var result = [];
 
  var headers=lines[0].split(",");
 
  for(var i=1;i<lines.length;i++){
 
     var obj = {};
     var currentline=lines[i].split(",");
 
     for(var j=0;j<headers.length;j++){
         obj[headers[j]] = currentline[j];
     }
 
     result.push(obj);
 
  }
  
  //return result; //JavaScript object
  return JSON.stringify(result); //JSON
}

If your columns contain commas in their values, you'll need to deal with those before doing the next step (you might convert them to &&& or something, then covert them back later).

A more elegant way to convert json to csv is to use the map function without any framework:

var json = json3.items
var fields = Object.keys(json[0])
var replacer = function(key, value) { return value === null ? '' : value } 
var csv = json.map(function(row){
  return fields.map(function(fieldName){
    return JSON.stringify(row[fieldName], replacer)
  }).join(',')
})
csv.unshift(fields.join(',')) // add header column
 csv = csv.join('\r\n');
console.log(csv)

Output:

title,description,link,timestamp,image,embed,language,user,user_image,user_link,user_id,geo,source,favicon,type,domain,id
"Apple iPhone 4S Sale Cancelled in Beijing Amid Chaos (Design You Trust)","Advertise here with BSA Apple cancelled its scheduled sale of iPhone 4S in one of its stores in China’s capital Beijing on January 13. Crowds outside the store in the Sanlitun district were waiting on queues overnight. There were incidents of scuffle between shoppers and the store’s security staff when shoppers, hundreds of them, were told that the sales [...]Source : Design You TrustExplore : iPhone, iPhone 4, Phone","http://wik.io/info/US/309201303","1326439500","","","","","","","","","wikio","http://wikio.com/favicon.ico","blogs","wik.io","2388575404943858468"
"Apple to halt sales of iPhone 4S in China (Fame Dubai Blog)","SHANGHAI – Apple Inc said on Friday it will stop selling its latest iPhone in its retail stores in Beijing and Shanghai to ensure the safety of its customers and employees. Go to SourceSource : Fame Dubai BlogExplore : iPhone, iPhone 4, Phone","http://wik.io/info/US/309198933","1326439320","","","","","","","","","wikio","http://wikio.com/favicon.ico","blogs","wik.io","16209851193593872066"

Update ES6 (2016)

Use this less dense syntax and also JSON.stringify to add quotes to strings while keeping numbers unquoted:

const items = json3.items
const replacer = (key, value) => value === null ? '' : value // specify how you want to handle null values here
const header = Object.keys(items[0])
const csv = [
  header.join(','), // header row first
  ...items.map(row => header.map(fieldName => JSON.stringify(row[fieldName], replacer)).join(','))
].join('\r\n')

console.log(csv)