Variable Scope in node.js/express.js

Question

I'm using express/node now and I have the following

   app.use(useridDetect);
   function useridDetect (request, response, next) {
        var myurl = url.parse(request.url);
        if (myurl.pathname === "/cookie") {
        var i = request.url.indexOf('?');
        query = request.url.substr(i+4, 32);
        //set userid
        next(); 
        } else {
            next(); // keep the middleware chain going
        }
    }


    app.use(require('./middleware/im')({
       userid: query,
       maxAge: 30 * 1000,
       reapInterval: 20 * 1000,
       authentication: require('./libs/authentication/' + AUTH_LIBRARY)
    }));

Now it says query is undefined in the second part(Obvious I can't do this...) But how can I make the second function access that variable without using global variable? Since I will have multiple people using this script and too many global vars might be a bad idea.

where/how exactly is the 'second part' called? Also am I correct to assume that the second part is the second app.use? — nemo
– nemo, Commented Oct 2, 2013 at 23:45
@nemo Yeah, they are all in app.js; And the 'second' part is referring to 'app.use(require('./middleware/im')({'... — Steve_bing
– Steve_bing, Commented Oct 2, 2013 at 23:47

Jason LeBrun · Accepted Answer · 2013-10-02 23:50:55Z

1

Each middleware that you define gives you a chance to read request information and modify the request/response objects. Rather than setting a variable called query, you should add a query field to you request object, and then have middleware/im's request handler look for that field in the request object.

However, note that Express already does query string parsing for you[1], so you shouldn't even need the userIdDetect middleware function. Just have middleware/im's request handler look in the object in `req.query, which should already contain a field named whatever the query string parameter was named.

[1] http://expressjs.com/api.html#req.query

answered Oct 2, 2013 at 23:50

Jason LeBrun

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