Callback / asynchronous request in nodejs - node.js

Question

I do a http request in nodejs with the following code
var buffer = "";
var postToPHP = function(data, path){
var httpreq = require('http');
var querystring = require("querystring");
var data = querystring.stringify(data);
var options = {
host : 'localhost',
path : path,
method : 'POST',
headers : {
'Content-Type' : 'application/x-www-form-urlencoded',
'Content-Length' : data.length
}
};
var buffer = "";
var reqPost = httpreq.request(options, function(res) {
res.on('data', function(d) {
buffer = buffer+d;
});
res.on('end', function() {
console.log("buffer",buffer); //this logs the buffer correctly
return buffer;
});
});
reqPost.write(data);
reqPost.end();
}
var buffer = postToPHP(message,path); //this buffer displays nothing because the call is async
I'd like to know exactly what is the standard procedure to "wait" for the server response in the nodejs or how to implement a callback that would react accordingly to what I want after I receive the message... Could someone give me an example of a callback on this please?

Answer 1

You have to pass in a callback if you're performing an asynchronous task inside a function:
var http = require('http'),
querystring = require('querystring');
function postToPHP(data, path, cb) {
var data = querystring.stringify(data);
var options = {
host: 'localhost',
path: path,
method: 'POST',
headers: {
'Content-Type': 'application/x-www-form-urlencoded',
'Content-Length': Buffer.byteLength(data.length)
}
};
http.request(options, function(res) {
var buffer = '',
calledBack = false;
res.on('data', function(d) {
buffer += d;
}).on('error', function(err) {
if (!calledBack) {
calledBack = true;
cb(err);
}
}).on('end', function() {
if (!calledBack) {
calledBack = true;
cb(null, buffer);
}
});
}).on('error', function(err) {
if (!calledBack) {
calledBack = true;
cb(err);
}
}).end(data)
}
Then use it:
postToPHP({ foo: 'bar' }, '/foo', function(err, data) {
if (err) throw err;
console.dir(data);
});