javascript - XMLhttpRequest with a node js server with express -

for reason don't know can't use xmlhttprequest in local server created in node js , express. let me show you... here server in node js:

var  express = require('express'), app = express.createserver();  app.get('/count', function(req, res) {     res.type('text/plain');     res.write('hello!')      res.end(); });  app.listen(4003); 

and runs jus fine! when acess localhost:4003/count see "hello!".

now server o.k, let's check html page:

<script>  var xmlhttp = new xmlhttprequest(); var resp = "" xmlhttp.onreadystatechange = function() {     if (xmlhttp.readystate==4 && xmlhttp.status==200){         resp = xmlhttp.responsetext;         } }  var cam = "localhost:4003/count"   function show(){     xmlhttp.open("get",cam,  true);     xmlhttp.send();     alert(resp); }  </script>  <center><h1><div style="color:#339966"> <input type="button" value="return of /count" onclick="javascript:show()"> </div> </h1> 

so, don't work =[, i've tried to:

• change localhost:4003/count value of variable cam, http://localhost:4003/count, 127.0.0.1:4003/count.
• open in firefox, safari , chrome.
• when try see xmlhttp.status alert() shows '0'. (but page open in browser)

along timing issues morgan covered...

• when including host in url, needs prefixed //.

  var cam = "//localhost:4003/count"; 

  otherwise, it'll treated relative path localhost:4003 directory name.

• you have deal same-origin policy when using ajax.

  so, if you're trying use file:// page, won't typically work well. file protocol doesn't have origin, can't pass sop, resulting in errors similar to:

  origin null not allowed access-control-allow-origin. 

  the easiest solution serve page application.

  you can either static() middleware.

  // `get /` serve `./public/index.html` app.use(express.static(__dirname + '/public')); 

  or route sends file itself.

  app.get('/', function (req, res) {     res.sendfile(__dirname + '/public/index.html'); }); 

  then, access page from:

  http://localhost:4003/ 

• also, both page , count served same origin, url can relative-from-root:

  var cam = "/count";