Using bluebird promises

js:scripts:bluebird.js

#!/usr/bin/env node

/**
Demostrate a practical use case with Bluebird promise api.
Read a line delimited file and store into sqlite3 db.

Promise.promisifyAll -  Converting synchromous api's to Async.
Promise.using and Promise.disposer - Resource managment.
Promise.map and Promise.spread - Leveraging arrays in promises. 

Notes:
1. You can forget everything but always remember to return something from callbacks !
2. I am prefferring named function expression over anoymous functions as it is easy to 
    ready and meaningful while debugging.

see:

http://bluebirdjs.com/docs/api
http://bluebirdjs.com/docs/api/disposer.html
see http://bluebirdjs.com/docs/api/promise.map.html

https://github.com/grumdrig/node-sqlite
**/

var fs = require('fs'),
    path = require('path'),
    Promise = require('bluebird'),
    // Promisify all functions with async support.
    sqlite3 = Promise.promisifyAll(require('sqlite3').verbose()),
    patternUser = new RegExp("\\w*\\.\\w*"),
    currentTime = new Date().getTime();

function fileRead(dir, file) {
    // we can do this for kicks, Promise.promisify(fs.readFileSync)
    return fs.readFileSync(path.join(dir, file), 'utf8', function(err, data) {
        console.log(err + "err");
        return data;
    });
}

// Read a file containing user names, \n delimited. Filter out bad names.
var data = fileRead("/Users/dhval", "users.txt").split(/\n/)
    .filter(function(user) {
        return patternUser.test(user);
    }).map(function(user) {
        return user.replace(/[^a-zA-Z0-9.]/g, "");
    });

// Returns a promise of user count with the given user name.
function userExists(con, userName) {
    var promise = con.getAsync("select count(*) as count from user where user = ?", userName).then(function(row) {
        return row.count;
    }, function(err) {
        console.log(err);
        return -1;
    });
    return promise;
}

// Returns a promise of new connection.
function createConnection(dbFile) {
    var connection = new sqlite3.Database(dbFile);
    // Making sure a table exists or create one. By returning a connection we avoid anti pattern of creating promise within promise.
    return connection.runAsync("CREATE TABLE if not exists user (id INT, user TEXT, pwd TEXT, createDt INT, updateDt INT)").then(function() {
        return connection;
    });
}

// Attaches a disposer to a promise. 
function getConnection(dbFile) {
    return createConnection(dbFile).disposer(function(connection, promise) {
        if (connection) {
            console.log("closing db connection, success=" + promise.isFulfilled());
            connection.close();
        }
    });
}

// You can see from logs that everythinng happen in proper sequence. Still it has a race condition because of dirty reads.
Promise.using(getConnection('users.db'), function(connection) {
    // Promise.dispose will be fired whenever we 'complete()' this promise. 
    var promise = new Promise(function(complete, reject) {
        var stmt = connection['stmt'] = connection.prepare("INSERT INTO user(user, createDt) VALUES (?,?)");
        console.log("count#" + data.length);
        Promise.map(data, function(userId) {
            return connection.getAsync("select count(*) as count from user where user = ?", userId).then(function(row) {
                console.log("got results: " + userId + "#" + row.count);
                return row.count ? row.count : 0;
            }).then(function(count) {
                if (count == 0) {
                    console.log("insert, " + userId);
                    return stmt.runAsync(userId, currentTime);;
                } else {
                    // it is a good habbit to return something from callbacks.
                    return true;
                }
            });
        }).spread(function() {
            console.log("complete, calling disposers");
            stmt.finalize();
            complete();
        }).catch(function(e) {
            console.log(e);
        })
    });
    return promise;
});

js:scripts:package.json

{
  "name": "js-dev",
  "version": "1.2.0",
  "description": "cmd line JS scripts.",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "bluebird": "^3.0.0",
    "sqlite3": "^3.1.0"
  }
}

react-online.js

<html>
    <head>
        <title>Hello World</title>
        <script src="https://unpkg.com/react@15/dist/react.js"></script>
        <script src="https://unpkg.com/react-dom@15/dist/react-dom.js"></script>
    </head>
    <body>
        <div id="root"></div>

        <script>
            window.onload = function()
            {
                class Greetings extends React.Component
                {
                    render()
                    {
                        return React.createElement('h1', null, 'Greetings, ' + this.props.name + '!');
                    }
                }
                ReactDOM.render(
                    React.createElement(Greetings, { name : 'User' }),
                    document.getElementById('root')
                );
            };
        </script>
    </body>
</html>