I'm new to node.js, I met a strange issue when run a simple sample.

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

var server = http.createServer(function(request, response){ 
    console.log('Connection');
    var path = url.parse(request.url).pathname;
    console.log(1);
    switch(path){
        case '/':
            response.writeHead(200, {'Content-Type': 'text/html'}); 
            response.write('hello world');
            break;
        case '/socket.html':
            console.log(2);
            fs.readFile(__dirname + path, function(error, data){
                if (error){
                    response.writeHead(404);
                    response.write("opps this doesn't exist - 404");
                    console.log(3);
                }
                else{
                    response.writeHead(200, {"Content-Type": "text/html"});
                    response.write(data, "utf8");
                    console.log(4);
                }
            });
            break;
        default:
            response.writeHead(404);
            response.write("opps this doesn't exist - 404");
            break;
    }
    console.log(5);
    response.end(); 
}); 

server.listen(8001); 

when I visit

http://localhost:8001/socket.html

backend log output as following:

    Connection
    1
    2
    5
    4
    Connection
    1
    5

In the browser, there is no output, the source of html is empty. Notice the log, I guess this maybe the response has already closed after log print "5", before log print "4".

I can't understand why the log sequence is not "1245", could somebody explain this to me?

I'm new to node.js, I met a strange issue when run a simple sample.

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

var server = http.createServer(function(request, response){ 
    console.log('Connection');
    var path = url.parse(request.url).pathname;
    console.log(1);
    switch(path){
        case '/':
            response.writeHead(200, {'Content-Type': 'text/html'}); 
            response.write('hello world');
            break;
        case '/socket.html':
            console.log(2);
            fs.readFile(__dirname + path, function(error, data){
                if (error){
                    response.writeHead(404);
                    response.write("opps this doesn't exist - 404");
                    console.log(3);
                }
                else{
                    response.writeHead(200, {"Content-Type": "text/html"});
                    response.write(data, "utf8");
                    console.log(4);
                }
            });
            break;
        default:
            response.writeHead(404);
            response.write("opps this doesn't exist - 404");
            break;
    }
    console.log(5);
    response.end(); 
}); 

server.listen(8001); 

when I visit

http://localhost:8001/socket.html

backend log output as following:

    Connection
    1
    2
    5
    4
    Connection
    1
    5

In the browser, there is no output, the source of html is empty. Notice the log, I guess this maybe the response has already closed after log print "5", before log print "4".

I can't understand why the log sequence is not "1245", could somebody explain this to me?

• javascript
• node.js

1 Answer 1

The fs.readFile method is asynchronous. When you call it, execution continues immediately after it (at the break statement), and then proceeds to the console.log(5), and the response.end() calls.

Therefore, response.end() is being called before the fs.readFile callback gets a chance to execute. You need to move the response.end() call inside the callback.