http.createServer的Node.js回调类型错误

Question

I am very new to node.js, and was playing around with a few tutorials and stumbled across this problem doing a little refactoring.

The tutorial I was following is linked here: http://www.tutorialspoint.com/nodejs/nodejs_web_module.htm

I decided to split out the callbacks to make the code a little more readable, so created a file reader method and a 'monitor' method:

function monitor(request, response)
{
        var pathname = url.parse(request.url).pathname;

        fs.readFile(pathname.substr(1), reader() );
}

http.createServer(monitor()).listen(8080);

When I run this I get the following error:

    var pathname = url.parse(request.url).pathname;
                                    ^

TypeError: Cannot read property 'url' of undefined
    at monitor

Clearly this is a type issue. I was looking into casting to http.incomingMessage, but am not familiar enough with javascript and my web searching did not yield a quick solution.

Thanks!

Answer 1

Your problem is in this line:

http.createServer(monitor()).listen(8080);

It should be:

http.createServer(monitor).listen(8080);

The reason is because you want to pass the monitor function as a callback, not call it. Placing the parenthesis after monitor will call the function with no arguments. When arguments are not given to the function, they take on the value undefined , hence the error you're getting.