CODEWITHSUNDEEP
javascriptnode.js
LinDan ChongWei
LinDan ChongWei

Reputation: 193

Need help understanding Node.js in respect to routing using a JavaScript API?

I understand the basics of routing in Node.js and using the http module for it. I understand all the Node.js code below but just the JavaScript API part and how it is used to make the routing code much more cleaner is what I have trouble understanding. When I say "trouble understanding" I mean trouble understanding the syntax and how the routes object is used.

The code is from an E-book I have been learning from so please read the code below.

var http = require("http"); 
var url = require("url");

var route = {   
  routes : {},
  for: function(path, handler){    
    this.routes[path] = handler;  
  } 
};

route.for("/start", function(request, response){    
  response.writeHead(200, {"Content-Type": "text/plain"});    
  response.write("Hello");    response.end();  
});

  route.for("/finish", function(request, response){    
    response.writeHead(200, {"Content-Type": "text/plain"});    
    response.write("Goodbye");   
    response.end();  
  });

function onRequest(request, response) {  
  var pathname = url.parse(request.url).pathname;  
  console.log("Request for " + pathname + " received.");  
  if(typeof route.routes[pathname] ==='function'){    
    route.routes[pathname](request, response);  
  }else{    
    response.writeHead(404, {"Content-Type": "text/plain"});    
    response.end("404 Not Found");  
  } 
}

http.createServer(onRequest).listen(9999); 
console.log("Server has started.")

My understanding so far is that: route.routes is an empty object and route.for is a function. The function has two parameters function(path,handler) but I don't understand the part in the function i.e. this.routes[path] = handler;

From my understanding this.routes[path] is an empty object so is the code setting handler to an empty object?

and beyond this I have absolutely no clue what function onRequest(request,response){}; is doing.

Plase explain the whole code for me as I find it very disturbing not being able to understanding the basics before progressing through the E-book.

Upvotes: 0

Views: 82

Answers (1)

Muhammad Umer
Muhammad Umer

Reputation: 18097

Http module that you include in first line has createserver function that takes a function as a parameter. In of the last lines we pass "onRequest" function to it. The function passed is internally invoked by http module whenever request is recived on port 9999 as also defined. Function onRequest is invoked with two parameters one is "request" that contains data like headers and body of a request that was recived. 2nd parameter is respons object it is whats sent back. It has functions that facilate this like writeHead which writes headers, .end which signals http module to sned the response finally back.

onRequest function can do whatever it wants with the request and send whatever response it wants to send back.

Here it using url module that is native to nodejs parses url and extract pathname which is everything after first / so www.mydomain.com/thispart/andthis...etc are extracted.

Then thus is done to do object lookup inside the routes. If object with key that is equal to string of this pathname exists it will return the value that is the function and if not the expression will evaluate to false and 404 part will be run. Upon match function gets invoked with response and request objects that onRequest got in the parameters.

In Javascript property of an object can be set even if its not present..

var a = {n:1};
a.x = "exists";
console.log (a.x); //exists

Upvotes: 1

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