node.js: confusion with order of callbacks - node.js

Question

I have just started with node.js. I find the asynchronous coding style it uses to be very impressive indeed. However, for those of us who are used to Java and Python it does take some time to get used to it.
I know the following code works fine. This is verified by several questions on this forum. I have also tried it on my own.
var http = require('http'),
fs = require('fs');
fs.readFile('./index.html', function (err, html) {
if (err) {
//throw err;
}
http.createServer(function(request, response) {
console.log("Server started");
response.writeHeader(200, {"Content-Type": "text/html"});
response.write(html);
response.write("Other things");
response.end();
}).listen(3000);
});
The way I am interpretting this is as follows:
1. Try reading the html file
i. When done create a server
ii. Send it over to the client
2. Do everything else.
However, we can also have a chain of thoughts as follows:
1. Create the server
2. Try reading the file
i. When done. Send it over to the client
3. In the meanwhile do anything else the server might be asked to do.
The code corresponding to the second chain of thoughts is:
var http = require('http'),
fs = require('fs');
http.createServer(function(request, response) {
console.log("Server started");
response.writeHeader(200, {"Content-Type": "text/html"});
fs.readFile('./index.html', function (err, html) {
if (err) {
//throw err;
}
response.write(html);
response.write("Other things");
});
response.end();
}).listen(3000);
While the first code works as expected. The second one displays nothing at all in the browser.
Why is the second chain of thoughts wrong?

Answer 1

Actually, what happens here is that the following function gets called each time there is an incoming request:
function(request, response) {
console.log("Server started");
response.writeHeader(200, {"Content-Type": "text/html"});
response.write(html);
response.write("Other things");
response.end();
}
You replaced that with:
function(request, response) {
console.log("Server started");
response.writeHeader(200, {"Content-Type": "text/html"});
fs.readFile('./index.html', function (err, html) {
if (err) {
//throw err;
}
response.write(html);
response.write("Other things");
});
response.end();
}
Now here, it will run the following:
Write the header
Queue the readFile
Immediately execute the following: response.end();
By the time it is done reading the file and wants to write the contents, you already ended the response