missing output

lib/index.js

 var fs = require('fs');
 var xlsx = require('xlsx');
-var cvcsv = require('csv');
 var mime = require('mime');
 exports = module.exports = XLSX_json;
 
@@ -24,8 +23,17 @@ function XLSX_json(config, callback) {
 
 function CV(config, callback) {
     var wb = this.load_xlsx(config.input)
-    var csv = this.to_json(wb);
-    return  callback(null,csv);
+    var json = this.to_json(wb);
+    var output = config.output;
+    if (config.output !== null) {
+        var stream = fs.createWriteStream(output, {
+            flags: 'w'
+        });
+        stream.write(JSON.stringify(json));
+        return callback(null, json);
+    } else {
+       return callback(null, json);
+    }
 }
 
 CV.prototype.load_xlsx = function(input) {