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Question

I have a simple app with two custom modules

app.js:

var mappings = require('./mappings.js');
var actions = require('./actions.js');

http.createServer(function (req, res) {
    var alias = req.url.substring(1);
    console.log(req.url);
    console.log(alias);
    var mapping = mappings[alias] || {
        action: 'error',
        statusCode: 404,
        data: 'File not found'
    };
    actions[mapping.action](res,mapping);
}).listen(3000);

mappings.js:

var mappings = {
    'goloroden': {
        action: 'redirect',
        url: 'http://www.goloroden.de',
        type: 'permanent'
    },
    'polarbear': {
        action: 'download',
        url: 'http://www.goloroden.de/images/Logo.png',
        fileName: 'PolarBear.png',
        contentType: 'image/png',
        forceDownload: false
    },
    'portrait': {
        action: 'download',
        url: 'file://./DSC_1067-2.jpg',
        contentType: 'image/jpeg',
        forceDownload: false
    }
};

module.exports = mappings;

actions.js:

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

var deliverDownload = function (res, mapping, data) {
    var contentDisposition = 
    mapping.forceDownload ? 'attachement' : 'inline';
    res.writeHead(data.statusCode, {
        'Content-Type': mapping.contentType,
        'Content-Disposition': contentDisposition + '; filename=' + mapping.fileName + ';'
    });
    data.pipe(res);
};

var actions = {
 'download': function (res, mapping) {
     var options = url.parse(mapping.url);
     switch(options.protocol) {
         case 'http:':
            http.get(url.parse(mapping.url), function (data) {
            deliverDownload(res, mapping, data);
            });
            break;
         case 'file:':
            var data = fs.createReadStream(options.host + options.path);
            data.statusCode = 200;
            deliverDownload(res, mapping, data);
            break;
     }
 },
 'error': function (res, mapping) {
     res.writeHead(mapping.statusCode, {
         'Content-Type': 'text/html'
     });
     res.end(mapping.statusCode + ' ' + mapping.data);
 },
 'redirect': function (res, mapping) {
     var statusCode = mapping.type === 'permanent' ? 301 : 307;
     res.writeHead(statusCode, {
         'Location': mapping.url
     });
     res.end();
 }
};
module.exports = actions;

So when I try to start this example, I get this error: ReferenceError: http is not defined. But i can't understand why. http is required in actions.js Do I have to call it in app.js too? if yes, why ?

Answer 1

You will have to because you didn't export the http module in your actions.js .

You exported actions which is:

var actions = {
 'download': function (res, mapping) {
     var options = url.parse(mapping.url);
     switch(options.protocol) {
         case 'http:':
            http.get(url.parse(mapping.url), function (data) {
            deliverDownload(res, mapping, data);
            });
            break;
         case 'file:':
            var data = fs.createReadStream(options.host + options.path);
            data.statusCode = 200;
            deliverDownload(res, mapping, data);
            break;
     }
 },
 'error': function (res, mapping) {
     res.writeHead(mapping.statusCode, {
         'Content-Type': 'text/html'
     });
     res.end(mapping.statusCode + ' ' + mapping.data);
 },
 'redirect': function (res, mapping) {
     var statusCode = mapping.type === 'permanent' ? 301 : 307;
     res.writeHead(statusCode, {
         'Location': mapping.url
     });
     res.end();
 }
};

When you say var someModule = require('someModule') you are including whatever was exported in someModule when it does module.exports = ...;

So in app.js your actions var is an object with download , error , and redirect functions.

Answer 2

Yes you do. Each module has its own scope, and variables defined in them aren't available outside the module unless you add it to module.exports . When you require something, you are simply creating a variable, and it's subject to all the normal scoping rules.

If this is confusing, you might want to read over the Node module documentation .