Node.js double console.log output

问题

I'm learning Node.js and I'd like to understand the "why" when code spits out duplicated console.log outputs but only a single response.write outputs.

Heres my simple code example:

var http = require('http');

http.createServer(function(request, response){
    response.writeHead(200, {'Content-type': 'text/plain'});
    console.log('hello 1');
    response.write('Hello world');
    console.log('hello 2');
    response.end();
}).listen(8000);

And on my console/terminal I get:

hello 1

hello 2

hello 1

hello 2

Thanks.

回答1:

Some browsers also send a request to locate the favicon.ico file. Since the file isn't present by default, a browser(Chrome in particular) will always send two requests: one for the originally requested file and another for favicon.ico. This is a known bug in Chrome and has been fixed in version 29. Firefox, however, requests for favicon.ico only for the first request. If you console.log the request URI path, you must see a request to localhost:8000/favicon.ico.

var http = require('http');

http.createServer(function(request, response){
    response.writeHead(200, {'Content-type': 'text/plain'});
    if(request.url === '/favicon.ico') {
        console.log('Favicon was requested');
    }
    console.log('hello 1');
    response.write('Hello world');
    console.log('hello 2');
    response.end();
}).listen(8000);

回答2:

I've had the same problem myself, and I found out that using something like

var http = require('http');
http.createServer(function(req,res) {
    if(req.url === '/favicon.ico')
    {
        //everything here is ignored
    }
    res.writeHead(200,{"Content-Type": "text/plain"});
res.write("Hello World\n");
res.end();
console.log("Connection made");
}).listen(1337, "127.0.0.1");
console.log("Server running at http://127.0.0.1:1337/");

is enough to avoid that behaviour. For some reason, when I check req.url and compare it to '/favicon.ico' nothing is sent to console, in fact, everything in that block is ignored. I don't know if this behaviour is expected, but you sure could try it.

回答3:

If you output the header you're telling the server that you found favicon, hence the response is processed and no matter what you get that double console.log(). Instead, end it before sending a writeHead() or send a 404.

var http = require('http');

http.createServer(function (req, res) {
    if(req.url === '/favicon.ico') {
        res.writeHead(404);
        res.end();
    } else {
        res.writeHead(200, {'Content-Type': 'text/plain'});
    }
    //code here...

    res.end();
}

回答4:

in a nutshell the duplication as it is mentioned before is a result of the favicon request so to avoid this problem, I propose you this simple snipet:

var pathname = url.parse(request.url).pathname;
if(pathname != '/favicon.ico')
console.log('hello 1');

回答5:

It can also be a Chrome plugin like JSONView. I was just trying to figure it out until I tried incognito and realized it was no longer causing the problem. Also was requesting a JSON file.

回答6:

i think that this problem still persists in chrome Version 67.0.3396.87 (32-bit) because when i ran my nodeJS script i saw 2 console.log() statements one was able to print out the query the other was not, so i corrected my code so as to see console.log() statements only once, it was simple all i had to do was add a return statement if the request.url was == (equal to)"/favicon.ico" in the beginning of the code and everything worked fine

previous code

var http = require('http');
var url = require('url');
http.createServer((request,response)=>{
var q = url.parse(request.url,true).query;
console.log(request.url);
console.log('hey there! we got a request from '+q.name+' !');
}).listen(8080);

and the output was :

/?name=harshit
hey there we got a request from harshit !
/favicon.ico
hey there we got a request from undefined !

code after debugging :

var http = require('http');
var url = require('url');
http.createServer((request,response)=>{
if(request.url == "/favicon.ico"){
return ;
}
var q = url.parse(request.url,true).query;
console.log(request.url);
console.log('hey there! we got a request from '+q.name+' !');
}).listen(8080);

output :

/?name=harshit
hey there we got a request from : harshit !

来源：https://stackoverflow.com/questions/17952436/node-js-double-console-log-output

标签

node.js

console.log