Dispatcher with Node JS

Question

Dispatcher with Node JS

I'm trying to do a simple server answering to url /page1 and /page2; this is the module dispatcher.js:

var HttpDispatcher = function() {


this.listeners = { get: [ ], post: [ ] }; 
  this.errorListener = function() { } 
} 

HttpDispatcher.prototype.on = function(method, url, cb) {

  this.listeners[method].push({
    cb: cb,
    url: url 
  }); 
}

HttpDispatcher.prototype.onGet = function(url, cb) {
  this.on('get', url, cb); 
}

HttpDispatcher.prototype.onPost = function(url, cb) {
  this.on('post', url, cb); 
}

HttpDispatcher.prototype.onError = function(cb) {
  this.errorListener = cb; 
}

HttpDispatcher.prototype.dispatch = function(req, res) {

  var parsedUrl = require('url').parse(req.url, true);
  var method = req.method.toLowerCase();

  if(this.listener[method][parsedUrl.pathname]) this.listener[method][parsedUrl.pathname](req, res)
  else this.errorListener(req, res); 
}

module.exports = new HttpDispatcher();

and this is the server:

var dispatcher = require('./node_modules/httpdispatcher');
var http = require('http');

dispatcher.onGet("/page1", function(req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Page One'); 
}); 

dispatcher.onPost("/page2", function(req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Page Two'); 
}); 

http.createServer(function (req, res) {
  dispatcher.dispatch(req, res);
}).listen(80, '127.0.0.1');

But when i try to execute the server, i get the error:

D:\Works\Web Resources\NODE JS\node_modules\httpdispatcher.js:33
if(this.listener[method][parsedUrl.pathname]) this.listener[method][parsedUr ^ TypeError: Cannot read property 'get' of undefined

Anyone knows why?

node.js

Answer 1

It may be a typo

if(this.listener[method][parsedUrl.pathname]) this.listener[method][parsedUrl.pathname](req, res)

I think it is this.listeners (with -s)

2nd question (from comments):

HttpDispatcher.prototype.on = function(method, url, cb) {
  this.listeners[method][url] = cb;
}

That way, you can check if URL exists (like you already do), and access the function like you already do.

Answer 2

Ok, the way you suggested works; i have one last question; i've added 3 console.log like this:

HttpDispatcher.prototype.dispatch = function(req, res) {

  var parsedUrl = require('url').parse(req.url, true);
  var method = req.method.toLowerCase();

  console.log(this.listeners[method][parsedUrl.pathname]); 

  if (this.listeners[method][parsedUrl.pathname]) 
    {
        this.listeners[method][parsedUrl.pathname](req, res);
        console.log('Found');
    }
  else 
    {
        this.errorListener(req, res); 
        console.log('ERROR LISTENER!');
    }
}

Now when i request the URL 127.0.0.1/page1 the message "Page One" is correctly displayied by the browser, but in the console i get:

[Function] Found undefined ERROR LISTENER!

So first the listener is found, but then is also called the errorListener; if i click to reload the page, on console i get just two more lines ([Function] and Found), no more ERROR LISTENER!... Do you know why the first time i load a page, even if i get the correct result in the browser, the dispatcher call also the erroListener?