Basic Ajax send receive with node js

Question

So I m trying to make a very basic node js server that with take in a request for a string  randomly select one from an array and return the selected string   Unfortunately I m running into a few problems   Here s the front end   function newGame        guessCnt 0     guess        server       displayHash       displayGuessStr       displayGuessCnt       function server        xmlhttp   new XMLHttpRequest        xmlhttp open  GET   server js   true      xmlhttp send        string xmlhttp responseText      This should send the request to server js   var http   require  http     var choices   hello world    goodbye world     console log  server initialized     http createServer function request  response        console log  request recieved        var string   choices Math floor Math random   choices length        console log  string      string      chosen        response on string       console log  string sent       listen 8001     So clearly there are several things going wrong here    I get the feeling the way I am  connecting  these two files isn t correct both in the xmlhttp open method and in using response on to send the string back to the front end  I m a little confused with how I call this page on localhost   The front end is named index html and the sever posts to 8001   What address should I be go to on localhost in order to access the initial html page after I have initialized server js  Should I change it to  listen index html  or something like that  are there other obvious problems with how I am implementing this  using  responsetext etc      sorry for the long multi-question post but the various tutorials and the node js source all assume that the user already has an understanding of these things

User · Answer

I was facing following error with code  nodejs 0 10 13   provided by ampersand   origin is not allowed by access-control-allow-origin  Issue was resolved changing  response writeHead 200    Content-Type    text plain       to   response writeHead 200                      Content-Type    text html                     Access-Control-Allow-Origin

User · Answer

RESTful API  Route   rtr route   testing    get  req  res   gt       res render  test       post  req  res  next   gt          res render  test       AJAX Code    function        anyid   on  click   function e       e preventDefault         ajax           url    testing           method   GET           contentType   application json           success  function res               console log  GET Request                            anyid   on  submit   function e       e preventDefault         ajax           url    testing           method   POST           contentType   application json           data  JSON stringify               info   quot put data here to pass in JSON format  quot                      success  function res               console log  POST Request

User · Answer

Here is a fully functional example of what you are trying to accomplish  I created the example inside of hyperdev rather than jsFiddle so that you could see the server-side and client-side code     View Code  https   hyperdev com    project destiny-authorization  View Working Application  https   destiny-authorization hyperdev space   This code creates a handler for a get request that returns a random string   app get   string   function req  res        var strings     string1    string2    string3       var n   Math floor Math random     strings length      res send strings n         This jQuery code then makes the ajax request and receives the random string from the server     get   string   function string          txtString   val string         Note that this example is based on code from Jamund Ferguson s answer so if you find this useful be sure to upvote him as well   I just thought this example would help you to see how everything fits together

User · Answer

Express makes this kind of stuff really intuitive  The syntax looks like below    var app   require  express   createServer    app get   string   function req  res        var strings     rad    bla    ska       var n   Math floor Math random     strings length      res send strings n      app listen 8001    https   expressjs com  If you re using jQuery on the client side you can do something like this     get   string   function string        alert string

User · Answer

Your request should be to the server  NOT the server js file which instantiates it  So  the request should look something like this  xmlhttp open  GET   http   localhost 8001    true   Also  you are trying to serve the front-end  index html  AND serve AJAX requests at the same URI  To accomplish this  you are going to have to introduce logic to your server js that will differentiate between your AJAX requests and a normal http access request  To do this  you ll want to either introduce GET POST data  i e  call http   localhost 8001  getstring true  or use a different path for your AJAX requests  i e  call http   localhost 8001 getstring   On the server end then  you ll need to examine the request object to determine what to write on the response  For the latter option  you need to use the  url  module to parse the request   You are correctly calling listen   but incorrectly writing the response  First of all  if you wish to serve index html when navigating to http   localhost 8001   you need to write the contents of the file to the response using response write   or response end     First  you need to include fs require  fs   to get access to the filesystem  Then  you need to actually serve the file   XMLHttpRequest needs a callback function specified if you use it asynchronously  third parameter   true  as you have done  AND want to do something with the response  The way you have it now  string will be undefined  or perhaps null   because that line will execute before the AJAX request is complete  i e  the responseText is still empty   If you use it synchronously  third parameter   false   you can write inline code as you have done  This is not recommended as it locks the browser during the request  Asynchronous operation is usually used with the onreadystatechange function  which can handle the response once it is complete  You need to learn the basics of XMLHttpRequest  Start here     Here is a simple implementation that incorporates all of the above   server js   var http   require  http          fs   require  fs         url   require  url     choices     hello world    goodbye world     http createServer function request  response       var path   url parse request url  pathname      if path    getstring            console log  request recieved            var string   choices Math floor Math random   choices length            console log  string      string      chosen            response writeHead 200    Content-Type    text plain             response end string           console log  string sent         else          fs readFile    index html   function err  file                  if err                         write an error response or nothing here                   return                                response writeHead 200     Content-Type    text html                    response end file   utf-8                           listen 8001   console log  server initialized      frontend  part of index html    function newGame        guessCnt 0     guess        server       displayHash       displayGuessStr       displayGuessCnt       function server        xmlhttp   new XMLHttpRequest       xmlhttp open  GET   http   localhost 8001 getstring   true      xmlhttp onreadystatechange function             if  xmlhttp readyState  4  amp  amp  xmlhttp status  200              string xmlhttp responseText                     xmlhttp send        You will need to be comfortable with AJAX  Use the mozilla learning center to learn about XMLHttpRequest  After you can use the basic XHR object  you will most likely want to use a good AJAX library instead of manually writing cross-browser AJAX requests  for example  in IE you ll need to use an ActiveXObject instead of XHR   The AJAX in jQuery is excellent  but if you don t need everything else jQuery offers  find a good AJAX library here  http   microjs com   You will also need to get comfy with the node js docs  found here  Search http   google com for some good node js server and static file server tutorials  http   nodetuts com is a good place to start     UPDATE  I have changed response sendHeader   to the new response writeHead   in the code above

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