ES6 Promise Examples

concat-with-callbacks.js

/**
 * @date     2015/3/21
 * @author   Dolphin<dolphin.w.e@gmail.com>
 *
 * Callback 风格的文件合并
 */

var fs = require('fs');

function getFilesInDir(dir, cb) {
    fs.readdir(dir, function (err, files) {
        if (err) {
            cb(err);
            return;
        }

        var jsFiles = files.filter(function (filename) {
            return filename.match(/\.js$/);
        }).map(function (filename) {
            return dir + '/' + filename;
        });

        cb(null, jsFiles);
    });
};

function readFiles(files, cb) {
    files = [].slice.call(files);

    var results = [],
        done = false,
        remain = files.length;

    files.forEach(function (path, index) {
        console.log('read file ' + path);

        fs.readFile(path, 'utf-8', function (err, data) {
            if (err) {
                done = true;
                cb(err);
                return;
            }

            results[index] = data;

            if (!done && !--remain) {
                done = true;
                cb(null, results);
            }
        });
    });
};

function output(options, contentList, cb) {
    var outputPath = options.output,
        banner = options.banner,
        separator = options.separator + '\n' || '\n';

    console.log('write file ' + outputPath);

    var content = contentList.join(separator);
    content = banner + '\n' + content;

    fs.writeFile(outputPath, content, 'utf-8', function (err) {
        if (err) {
            cb(err);
        }
    });
};

function concatJS(options, cb) {
    if (!options) {
        return cb(new Error('concat options is required'));
    }

    var writeFile = output.bind(null, options);

    getFilesInDir(options.path, function(err, files) {
        if (err) {
            return cb(err);
        }

        readFiles(files, function (err, contentList) {
            if (err) {
                return cb(err);
            }

            writeFile(contentList, function (err) {
                if (err) {
                    return cb(err);
                }
            });
        });
    });
};

module.exports = concatJS;

concat-with-promise.js

/**
 * @date     2015/3/21
 * @author   Dolphin<dolphin.w.e@gmail.com>
 *
 * Promise 风格的文件合并
 */

var fs = require('fs');

function getFilesInDir(dir) {
    return new Promise(function (resolve, reject) {
        fs.readdir(dir, function (err, files) {
            if (err) {
                reject(err);
                return;
            }

            var jsFiles = files.filter(function (filename) {
                return filename.match(/\.js$/);
            }).map(function (filename) {
                return dir + '/' + filename;
            });

            resolve(jsFiles);
        });
    });
};

function readFiles(files) {
    var promises = files.map(function (path) {
        return new Promise(function (resolve, reject) {
            console.log('read file ' + path);

            fs.readFile(path, 'utf-8', function (err, data) {
                if (err) {
                    return reject(err);
                }

                resolve(data);
            });
        });
    });

    return Promise.all(promises);
};

function output(options, contentList) {
    var outputPath = options.output,
        banner = options.banner,
        separator = options.separator + '\n' || '\n';

    console.log('write file ' + outputPath);

    return new Promise(function (resolve, reject) {
        var content = contentList.join(separator);
        content = banner + '\n' + content;

        fs.writeFile(outputPath, content, 'utf-8', function (err) {
            if (err) {
                reject(err);
                return;
            }

            resolve();
        });
    });
};

function concatJS(options) {
    if (!options) {
        return Promise.reject(new Error('concat options is required'));
    }

    var writeFile = output.bind(null, options);

    return getFilesInDir(options.path)
        .then(readFiles)
        .then(writeFile)
        .catch(function (err) {
            throw new Error(err);
        });
};

module.exports = concatJS;

test.js

/**
 * @date     2015/3/21
 * @author   Dolphin<dolphin.w.e@gmail.com>
 */


var fs = require('fs'),
    concatWithPromise = require('./concat-with-promise'),
    concatWithCallbacks = require('./concat-with-callbacks');

function makeFiles() {
    'abcdefg'.split('')
        .forEach(function (char) {
            fs.writeFileSync(
                'src/' + char + '.js',
                'console.log("this is ' + char + '.js");'
            );
        });
};

!fs.existsSync('src') && fs.mkdirSync('src'), makeFiles();
!fs.existsSync('dist') && fs.mkdirSync('dist');

console.log('========= Testing Promises =========\n');

concatWithPromise({
    path: 'src',
    output: 'dist/output-promise.js',
    banner: [
        '/*',
        ' * Generated with Promise',
        ' */'
    ].join('\n'),
    separator: '\n'
}).then(function () {
    console.log('\n========= Testing Callbacks =========\n');

    concatWithCallbacks({
        path: 'src',
        output: 'dist/output-callback.js',
        banner: [
            '/*',
            ' * Generated with Callbacks',
            ' */'
        ].join('\n'),
        separator: '\n'
    }, function (err) {
        console.log(err);
    });
}).catch(function (err) {
    console.log(err);
});