Error in updating an existing document field count in Elasticsearch

gistfile1.js

        var options = {
      			host: 'localhost',
    				port: '9200',
    				path: 'prototype_2013.01.03/chow-clfg/Nx4JcvyxTPujkyy0Jq5BNw/_update?parent=chow-demo',
    				method: 'POST'
    			};

          var script = 'ctx._source[\"chow-clfg\"].count+=num';
          var data = '{"script":"'+script+'","params":{"num":1}}';
    			data = JSON.parse(data);

    			var req = http.request(options, function(res){
  					res.setEncoding('utf8');
  					
  					res.on('data', function (chunk) {
  						console.log(chunk);
  					});
    			});

    			req.on('error', function(e) {
  					console.log('problem with request: ' + e.message);
				});
    			
    			req.write(data);
    			req.end();

// Returns result
{"script":"ctx._source["chow-clfg"].count+=num","params":{"num":1}}
                        ^
SyntaxError: Unexpected token c
    at Object.parse (native)
    at ElasticSearchCall.<anonymous> (/home/plumbline/Applications/nodejs/node-v0.8.14/prototype.js:136:20)
    at ElasticSearchCall.EventEmitter.emit (events.js:96:17)
    at IncomingMessage.ElasticSearchCall.exec (/home/plumbline/Applications/nodejs/node-v0.8.14/node_modules/elasticsearchclient/lib/elasticsearchclient/calls/elasticSearchCall.js:49:18)
    at IncomingMessage.EventEmitter.emit (events.js:126:20)
    at IncomingMessage._emitEnd (http.js:366:10)
    at HTTPParser.parserOnMessageComplete [as onMessageComplete] (http.js:149:23)
    at Socket.socketOnData [as ondata] (http.js:1367:20)
    at TCP.onread (net.js:403:27)