Question

I defined mysql connection with all parameters necessary to app.js, how can make visible to other scripts in routes/ by default, without requiring or redefining mysql parameters, just using client.query(..)?

Answer 1

You can inject mysql connection into other scripts like this:

app.js

var mysqlConnection = new Conection(params);
require('controller/main.js)(mysqlConnection);

main.js

module.exports = function(mysqlConnection) {
    // You can access your mysql connection here
};

UPDATE:

You can inject several variables same way. Also you still can export methods from module if you need this:

app.js

var mysqlConnection = new Conection(params);
var news = require('model/news.js)(app, mysqlConnection);
news.list(function(err, news) {
    // Do something
});

news.js

module.exports = function(app, mysqlConnection) {
    var methods = {};
    // mysql connection and app available from here
    methods.list = function(cb) {
        mysqlConnection.list(function(err, data) {
            cb(err, data);
        });
    };

    return methods;
};