tsconsole

To run this:

If you haven’t already:

1. install git from here.
2. install vscode from here.
3. install node.js from here.
4. npm install -g typescript
5. npm install -g ts-node

Install the code and dependencies for this project

1. git clone https://github.com/rhildred/tsconsole.git .
2. npm install to get the local dependencies for this project.

Aggregation

We made a new object to replace the javascript window.console. This object has 2 methods readLine(sPrompt: string) and log(sOut :string). These methods use 2 static classes from npm, readline-sync and fs for getting console input and synchronously writing to stdout (file handle 1).

import readlineSync = require('readline-sync');
import * as fs from 'fs';

export class Console{
    log(sOut : string){
        fs.writeSync(1, sOut + "\n");
    }
    readLine(sPrompt: string): string{
        return readlineSync.question(sPrompt);
    }
}

To use these objects we import them at the start of the file. As well as importing them we need to tell npm to resolve the dependency in the package.json file:

  "dependencies": {
    "@types/node": "^10.0.8",
    "@types/readline-sync": "^1.4.3",
    "readline-sync": "^1.4.9"
  }

The general pattern for aggregation from npm is to add the dependency and import it into the source file.

Inheritance

Once we have our object, we can inherit from that object to get it’s methods and properties. For instance:

import {Console} from './index' ;

export class ProductionConsole extends Console{
}

Now we can instantiate a ProductionConsole and readLine and log with it. The production console gets those methods by inheriting from the Console class.

Polymorphism

Inheritance is also called specialization. Our production console is a special console that only logs if we aren’t in production. We will override the log(sOut :string) method to have the desired new functionality.

    log(sOutput: string){
        if(this._bLogging){
            super.log(sOutput);
        }
    }

Encapsulation

A long with the overridden log method we also need to add a way to turn logging on and off. We add that to the object as well as a private attribute _bLogging . If we change the implementation consumers of the object don’t need to change. This is called encapsulation.

import {Console} from './index' ;

export class ProductionConsole extends Console{
    private _bLogging :boolean = false;
    logging(bLogging : boolean){
        this._bLogging = bLogging;
    }
    log(sOutput: string){
        if(this._bLogging){
            super.log(sOutput);
        }
    }
}

Saving logs on the cloud with Firebase

“I don’t always write code but when I do it always works on my machine.” (The most interesting coder in the world) Seriously, I need a way to debug my code when it is running in production and users find new and interesting ways to break it. To do this I will set up a folder in a firebase realtime database called logs. I will write messages in the folder that look like this:

{
    "-LC_Ebrb0gYX_5cl3r35": {
        "message": "Firebase initialized",
        "timestamp": "2018-05-15T19:19:44.354Z"
    },
    "-LC_EdeI5xai-QqGSlBL": {
        "message": "Hello World",
        "timestamp": "2018-05-15T19:19:51.699Z"
    },
    "-LC_EeKG893230dqeMsf": {
        "message": "You input 5",
        "timestamp": "2018-05-15T19:19:54.449Z"
    }
}

I am going to aggregate the firebase technology in my existing ProductionConsole.ts using the pattern that I established earlier.

import firebase = require("firebase-admin");
import * as url from "url";

These get firebase and url into my code. Then I update the package.json to include the implementing node module.

  "dependencies": {
    "@types/node": "^10.0.8",
    "@types/readline-sync": "^1.4.3",
    "firebase-admin": "^5.12.0",
    "readline-sync": "^1.4.9"
  }

I use the url module to split the host and path for initializing firebase:

    private _oUrl!: any;
    private _oRef!: firebase.database.Reference;
    log(sOutput: string) {
        if (this._bLogging) {
            super.log(sOutput);
        }
        if(this._oUrl) {
            this._oRef.push({message: sOutput, 
                timestamp: new Date().toISOString()})
        }
    }
    saveLog(sUrl: string) {
        this._oUrl = url.parse(sUrl);
        let serviceAccount = require("./privatekey.json");

        firebase.initializeApp({
            credential: firebase.credential.cert(serviceAccount),
            databaseURL: this._oUrl.protocol + "//" + this._oUrl.host
        });


        let db = firebase.database();

        this._oRef = db.ref(this._oUrl.pathname);

        this.log("Firebase initialized");
    }

Now when I run my code, I see the message “Firebase initialized” in both the console and the firebase. Next events!