Node.js gives unpredictable ajax response on the first time of startup

Question

I am using node.js as back end and canjs as front end library.

Node code:

var express = require('express');
var app = express();
var http = require("http");
var fs = require("fs");
var cons = require('consolidate')

app.configure(function(){
      app.engine('html', cons.handlebars);
      app.set('view engine', 'html');
      app.set('views', __dirname)
      app.use(express.favicon())
      app.use(express.logger('dev'))
      app.use(express.static(__dirname ))
      app.use(express.bodyParser())
      app.use(express.methodOverride())
      app.use(express.cookieParser("secret"))
      app.use(express.session({ secret: 'keyboard cat' }))
      app.use(app.router)
    });

app.init = function(){
    fs.readFile('./sample.json', 'utf8', function(error, data) {
        if (error) {
            throw(error);
        }
        else
            app.set("json", data);
    })};

app.get('/things', function(req, res){
    app.init();
    res.set('Content-Type', 'text/json');
    res.send(app.get("json"));
});

app.get('/things/:id', function(req, res){
    app.init();
    res.set('Content-Type', 'text/json');
    res.send((JSON.parse(app.get("json")))[req.param('id')]);
});

app.get('/main.html', function(req, res){
    app.init(function(error, data){
        if (error) {throw error}
        res.render('main.html');
    });
});

app.listen(3000);

Can.js code:

Todo = can.Model({
    findAll: "GET /things",
    findOne: "GET /things/{id}",
},{});

$(document).ready(function(){

    Todo.findAll({}, function(todos){
        console.log(JSON.stringify(todos));
    })

    Todo.findOne( { id: 1 }, function( todo ) {
        console.log( todo );
    })

});

HTML:

<script type="text/javascript" charset="utf-8" src="./jquery-1.8.2.js"></script>
<script type="text/javascript" charset="utf-8" src="./can.jquery-1.0.7.js"></script>
<script type="text/javascript" charset="utf-8" src="./can.fixture.js"></script>
<script type="text/javascript" charset="utf-8" src="./master.js"></script>

JSON:

{"0":{"id":1,"name":"do the dishes"},"1":{"id":2,"name":"go to dentist"},"2":{"id":3,"name":"go swimming"},"4":{"id":5,"name":"masturbate"}}

Each time the server is started up, the console will find the ajax GET response for both functions (findAll and findOne) returning either undefined or 500 error:

XHR finished loading: "http://localhost:3000/things". jquery-1.8.2.js:8416
undefined master.js:12

GET http://localhost:3000/things/1 500 (Internal Server Error) jquery-1.8.2.js:8416
XHR finished loading: "http://localhost:3000/things/1". jquery-1.8.2.js:8416
Uncaught TypeError: Function.prototype.apply: Arguments list has wrong type 

But if I refresh the page after this, the two functions will work normally, giving:

XHR finished loading: "http://localhost:3000/things". jquery-1.8.2.js:8416
{"0":{"id":1,"name":"do the dishes"},"1":{"id":2,"name":"go to dentist"},"2":{"id":3,"name":"go swimming"},"4":{"id":5,"name":"masturbate"},"length":0,"_namespace":".observe2"} master.js:12
XHR finished loading: "http://localhost:3000/things/1". jquery-1.8.2.js:8416
Constructor {name: "go to dentist", _data: Object, id: 2, _namespace: ".observe3"}
 master.js:16

What is GOING ON??

Answer 1

The problem is that you're calling app.get("json"); before its value has been set by the fs.readfile callback in app.init (which occurs sometime after the first call to app.init(); returns).

You should probably change your code to only call app.init once, and don't listen for requests until its work completes.

app.init = function(callback){
    fs.readFile('./sample.json', 'utf8', function(error, data) {
        if (error) {
            throw(error);
        } else {
            app.set("json", data);
            callback();
        }
    });
};

...

app.init(function() {
    app.listen(3000);
});