Javascript asynchronous sample

00. Resource.js

//Dummy resource
module.exports = {
    open: function() {

        var res = {
            read: function() {
                return new Promise(function(_resolve, _reject) {
                    setTimeout(function() {
                        _resolve('hogeeee');
                        //return _reject('read error!');
                    }, 1000);
                });
            },
            close: function() {
                console.log('Resource is closed.');
            }
        };

        return new Promise(function(resolve, reject) {
            setTimeout(function() {
                console.log('Resource is opened.');
                return resolve(res);
                //reject('open error!');
            }, 1000);
        });
    }
};

01. main-async.js

//since ES7 or NodeJS 7
var Resource = require('./00. Resource');

(async ()=> {
    const res = await Resource.open("path"); 
    
    try{
        const result = await res.read();
        
        console.log(result);
    }
    finally{
        res.close();
    }
})().catch((err)=> console.error((err&&err.stack) || err));

02. main-promise.js

const Resource = require('./00. Resource'); 

(function() {

    //Open resource.
    var res = Resource.open('path');

    //Read content from resource.
    var result = res.then(function(_res) { return _res.read(); });

    //Print result.
    result.then(function(_result) {
        console.log(_result);
    });

    //Close resource.
    Promise.all([res, result])
    .then(
        function() {
            res.then(function(_res) { _res.close(); });
        },
        function() {
            res.then(function(_res) { _res.close(); });
        }
    );

    //Print error.
    Promise.all([res, result]).catch(function(err) {
        console.error(err);
    });

})();

03. main-co.js

var Resource = require('./00. Resource');
var co = require('co');

co(function* () {

    var res = yield Resource.open('path');

    try {
        var result = yield res.read();
        console.log(result);
    } finally {
        res.close();
    }

})
.catch(function(err) { console.error(err); });