Programming Lessons

2024-09-17 - Classes and OOP

• Classes are bundles of data with functions attached
• The goal is to hide the insides from the rest of the world
  • simplifies big projects by keeping code and data close together
  • Prevents spaghetti code
  • Makes updates easier
  • "object-oriented design"
  • This is called encapsulation
• Classes can inherit other class' features (this is called inheritance
  • class Person
  • class Kid extends Person
  • You get all of the functions of the parent class, but the data is usually hidden for safety
  • You can override functions from the parent with your own version, and you can call the parent's version if you want to do that plus some more
  • Sometimes a parent class leaves a "fill-in-the-blank" function that you have to implement in order to extend it.
  • Some classes don't have any data, and don't implement any of their own functions. In that case, it's called an interface because all it does is make a promise.
    • Any class that implements my interface will do all of these things
    • You can put anything in a variable that holds an interface type as long as it implements the interface.
    • This is called polymorphism
• Programming that's based on encapsulatoin, inheritance, and polymorphism with classes is called Object-oriented because it uses objects as the main idea to organize code.
  • c++
  • typescript
  • java
  • gdscript
  • python
• There are other paradigms: functional, imperative, constraint-logic, and other weird ones.
  • Most modern languages are multi-paradigm, which means you can use ideas from more than one of these

Setting up a typescript project

Basically, just adapt this package.json file, then type npm i:

{
  "name": "",
  "type": "module",
  "version": "1.0.0",
  "description": "",
  "scripts": {
    "build": "npm run build-code && npm run build-bundle",
    "build-code": "tsc",
    "build-bundle": "esbuild build/main.js --sourcemap --bundle --outfile=dist/main.cjs --platform=node --format=cjs",
    "run": "node dist/main.cjs",
    "br": "npm run build && npm run run",
    "test": "jest"
  },
  "author": "Erik Lee",
  "license": "MIT",
  "homepage": "",
  "devDependencies": {
    "@babel/preset-env": "^7.25.4",
    "@babel/preset-typescript": "^7.24.7",
    "@jest/globals": "^29.7.0",
    "@types/node": "^22.5.4",
    "esbuild": "^0.23.1",
    "jest": "^29.7.0",
    "typescript": "^5.6.2"
  },
  "dependencies": {
    "source-map-support": "^0.5.21"
  }
}

Unit testing with jest

jest is a javascript test framework that makes it easy to test small parts of your code. You have to install it along with babel:

npm i --save-dev @jest/globals
npm i --save-dev @babel/preset-env
npm i --save-dev @babel/preset-typescript

Here's how it works:

// first you have to import the functions you'll need
import {test,expect} from '@jest/globals';

// Now you make tests
// first call test("a description of your test", () => {a function that does the testing})

test("Make sure true things are still true", () => {
    // expect is a function that takes a value and returns a test object. The test
    // object has a ton of methods that check different things about the value, like
    // equality to other values, truthiness, definedness, etc. So you call expect on 
    // the value, then tell it how to check to see if it's what you wanted.
    expect(true===true).toBeTruthy();
})