Node.js blocking versus non-blocking

• Download Blocking_versus_non_blocking.Node.js.ts.zip
• Download Events.Node.js.ts.zip

import * as file_system from 'fs';
import * as path from 'path';

const Blocking = () => {
    // Blocks here until 'Data.txt' file is read:
    const data: Buffer = file_system.readFileSync(path.resolve(__dirname, '..') + "/Data.txt");
    console.log(data.toLocaleString()); // 'Data' is displayed...
    console.info("This text appears *AFTER* 'Data'");
}

export default Blocking;

import * as file_system from 'fs';
import * as path from 'path';

const Non_blocking = () => {
    file_system.readFile((path.resolve(__dirname, '..') + "/Data.txt"), (error, data) => {
        if (error) throw error;
        console.log(data.toLocaleString()); // 'Data' is displayed...
    });
    console.info("This text appears *BEFORE* 'Data'");
}

export default Non_blocking;

import Blocking from './Blocking';
import Non_blocking from './Non_blocking';

(function Main() {
    console.clear();
    console.info("Executable file: " + __filename + "\n");
    Blocking();
    setTimeout((duration) => {
        console.info(duration + " elapsed...");
        Non_blocking();
    }, 2500, '2.5 sec.');
})();

Exercise

• Process two images in parallel with Sharp image processing library here…

Predefined event types identified by names like 'close', 'error', 'finish'… are available from (typed) resources like standard input, standard output….

(function Keyboard(information) {
    console.info(`${information}`);

    const output_stream = fs.createWriteStream(
        path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..') + "/Keyboard.txt");
    output_stream.on('error', (error) => console.info(`error: ${error.message}`));

    const input_stream = readline.createInterface({ // 'import readline from 'node:readline';'
        input: process.stdin,
        output: process.stdout,
        prompt: "Enter a sentence: "
    });
    input_stream.prompt();
    input_stream.on('line', (line) => {
        switch (line.trim()) {
            case 'exit':
                input_stream.close();
                break;
            default:
                output_stream.write(line + '\n');
                input_stream.prompt(); // Next sentence...
        }
    }).on('close', () => {
        output_stream.end();
        output_stream.on('finish', () => console.info("Sentences have been written to 'Keyboard.txt'..."));
        // Program stop (without error) is queued:
        setTimeout(() => process.exit(0));
    });
})("'Keyboard' app. started...");

Node.js offers a native event model, which in particular allows custom event emission and reception. An advanced event model is based on the RxJS library.

Event reception

// import {channel} from "./Input"; // Compilation...
import {channel} from "./Input.js"; // Execution...

channel.on('html', (html) => console.info("***\n" + html));

Event emission

import events from "node:events";
import fs from "node:fs";
import path from "node:path";
import {fileURLToPath} from "node:url";

export const channel = new events.EventEmitter();

(function Input(information) {
    console.info(`${information}`);
    const __dirname = path.dirname(fileURLToPath(import.meta.url));
    const input_stream: fs.ReadStream = fs.createReadStream(path.resolve(__dirname, '..') + "/index.html", 'utf8');
    input_stream.on('error', (error) => console.info(`error: ${error.message}`));
    input_stream.on('data', (html) => channel.emit('html', html));
})("'Events' app. started...");

export default class OpenSLR_org_88 { // https://gitlab.com/nicolasobin/att-hack
    …
    private static _Audio_file_processing(datum: any, audio_file_name: string): never | void {
        const audio_stream = file_system.createReadStream(OpenSLR_org_88.Path + audio_file_name);
        let audio = new Uint8Array;
        audio_stream.on('error', (error) => {
            throw new Error("Audio file extraction failed... " + error);
        });
        audio_stream.on('end', () => {
            datum.audio = audio;
            // File destruction?
            // file_system.unlink(OpenSLR_org_88.Path + audio_file_name, (error) => {
            //     if (error)
            //         console.error(OpenSLR_org_88.Path + audio_file_name + " audio file destruction failed... " + error);
            // });
        });
        audio_stream.on('data', (chunk) => {
            // console.assert(chunk instanceof Uint8Array && chunk.constructor.name === 'Buffer');
            // console.info(`Chunk of size ${chunk.length}... with raw data: ${chunk}`);
            // console.assert(audio.byteLength === audio.length);
            const _audio = new Uint8Array(audio.byteLength + chunk.length);
            _audio.set(audio); // Copy...
            _audio.set(chunk as Uint8Array, audio.byteLength); // Add...
            audio = _audio; // Update...
        });
    }
    …
}