- Node is a web server. Not a framework.
- Node has some built-in modules that we can use. One of them is called http, so lets import that now using require.
- In this code, we require a module for this JS file:
var http = require('http');
- Here, we are setting a variable http to the module http. Now all of 'http' module functions can be used by the variable.
- Now, one of those functions is to create a server:
http.createServer(function(request, response) {
// some stuff
});
- So, we create a server, added a 'callback' function, which will be described soon. We aren't done yet, because we haven't setup the port for the server to listen on. You do that like this:
http.createServer(function(request, response) {
// some stuff
}).listen(3000);
- Now, you can run this server by typing 'node index.js' in the console, and you have a server running! But...alas..it does nothing atm.
- Lets set a console log so we can see something happening:
console.log("Listening on port 3000");
- Now, if you stop the server (ctrl + c), and re run it, you will get a console output.
- So, lets go over whats happening here.
- We started a server on port 3000, and we get a console log output. NodeJS is non-blocking, meaning we can run code while other code is being run.
But, NodeJS is still a single-threaded server.
- We started a server on port 3000, and we get a console log output. NodeJS is non-blocking, meaning we can run code while other code is being run.
- It gets around this by using what's called a callback function:
http.createServer(function(request, response) {
// some stuff
});
- The function(request, response) is the callback function. This waits for a request and while it's waiting, it continues to execute code after the http.createServer block. So, a request would be visiting localhost:3000, which would then execute the callback function code. NodeJS also calls the way it waits for a request an Event Loop.
- When Node gets that request, it will now execute the callback function, and run that code. Let's do that now:
http.createServer(function(request, response) {
console.log("You have made a request to the node server on port " + port);
console.log("This is the response!");
console.log("The callback function is waiting for the request, and gives this response.");
}).listen(port);
-
So, if we run the server, we get the following
-
As you can see, we see "Listening on port 3000", but not the console.log within the callback function. We haven't made a request yet, so it won't be executed, and the REASON we see "Listening on port 3000", is because of the non-blocking code Node uses. We need to make a request to see the console.log inside the callback function. Go to localhost:3000, and you will now see:
