Streaming task-runner (how gulp works, simplified)

task-runner.js

'use strict';

const fs = require('fs');
const glob = require('glob').sync;
const mkdirp = require('mkdirp').sync;
const sass = require('node-sass');
const path = require('path');
const streams = require('stream');

const runner = {};

/**
 * Glob from source
 */
runner.src = function(globStr) {

    const fileQueue = glob(globStr);

    const rs = streams.Readable({ objectMode: true });
    rs._read = function() {

        const file = fileQueue.shift();
        if (file) {
            this.push({
                filename: file,
                contents: fs.readFileSync(file, { encoding: 'utf8' })
            });
        }

    };
    return rs;
};

/**
 * Save to destination
 */
runner.dest = function(basePath) {

    const ws = streams.Writable({ objectMode: true });
    ws._write = file => {

        mkdirp(path.dirname(basePath + file.filename));
        fs.writeFileSync(basePath + file.filename, file.contents);

    };
    return ws;
};

/**
 * Example Plugin: Sass
 */
const compileSass = function() {

    const ts = streams.Transform({ objectMode: true });
    ts._transform = function(file) {

        sass.render({ data: file.contents }, (err, result) => {
            file.filename = file.filename.replace(/\.scss$/, '.css');
            file.contents = result.css.toString();
            this.push(file);
        });

    };
    return ts;
};

/**
 * Usage
 */
runner.src('scss/*.scss')
    .pipe(compileSass())
    .pipe(runner.dest('css/'));