Summer Homework #2 💻 🥬

New stuff we learned this week: 🤔

TypeScript

functions that do not explicitly return anything should get the return type annotation of void:

function logHowdy(): void {
  console.log("Howdy!");
}

but undefined is a valid type as well, so if you explicitly return undefined you can declare that as well:

function returnsUndefined(): undefined {
  return undefined;
}

true and false are also types in TS, and can be used in any place you would use a normal type:

let name: string | false = "jared";
name = false;

function getLastName(name: string): string | true {
  if (name === "Beyonce") {
    return true;
  } else if (name === "Kiah") {
    return "Henderson";
  }
  return "Artinian";
}

specific strings are also valid types, which are especially useful in union types:

function returnsGoat(): "goat" {
  return "goat";
}

function orderStatus(orderId: string): "pending" | "paid" {
  if (orderId === "123abc") {
    return "pending";
  }
  return "paid";
}

you can create your own custom named types (the convention is to use PascalCase) like this:

type OrderStatus = "pending" | "paid";

tuples are arrays of defined width and type, and can by typed like this:

type PersonData = [string, number, boolean];

let jared: PersonData = ["Jared", 41, true];

function getWillow(): PersonData {
  return ["willow", 14, false];
}

objects can be declared as custom types by specifying the type of each property:

type Person = {
  name: string;
  hasBeard: boolean;
};

const win: Person = {
  name: "Winfield",
  hasBeard: false,
};

// as with all other types, you don't NEED to name the type
function getPet(): { type: string; name: string } {
  return {
    type: "turtle",
    name: "Stalin",
  };
}

Typescript is structurally typed — which means that “if it looks like a duck, walks like a ducks, talks like a duck…it’s a duck”. That means, for instance, that this works:

class Duck {
  name: string;
  beakLength: number;

  constructor(name: string, beakLength: number) {
    this.name = name;
    this.beakLength = beakLength;
  }
}

// 😎 LOOK! **classes** are also TYPES
function getDuckName(duck: Duck): string {
  return duck.name;
}

// this works because we're passing it an instance
getDuckName(new Duck("Daffy", 11));

// 😎 WORKS! It's not an instance of the `Duck` class
// but it has the same STRUCTURAL TYPE, so TS is OK 👍
getDuckName({ name: "Ducky", beakLength: 4 });

Javascript ES Modules

historically javascript has lacked a good module system for sharing code between multiple files.
because of this node adopted and popularized a function-based approach called commonjs which used module.exports and a require() function to share code between files.
TC39 (the committee responsible for the evolution of the javascript language) decided to add a new syntax for importing/exporting, called “ES Modules”. The syntax looks like this:

import fs from "fs";
import { createServer } from "http";
import { sayGoat } from "./my-goat-module";

instad of using module.exports, with ES Modules you use the new export keyword, like so:

export function sayGoat() {
  console.log("goat");
}

Useful Links:

Homework Plan (next class in 3 weeks)

1 day (per week) review all flashcards
1 day (per week) touch typing practice
1 day Typescript Homework
1 day Bash Variable review Assignment
more coming soon…

Homework (week 1)

review all flashcards

touch typing practice

Watch CCCS

Typescript Homework

Homework (week 2)

review all flashcards

touch typing practice

bash variable assignment

Typescript Assignment

very carefuly and slowly review the Typescript portion of “New Stuff” above ^^.
go to https://gitlab.howtocomputer.link/htc/ts-intro-2, fork it, then clone it into ~/node/summer-2 through ssh, then connect to the dir through vscode.
create a new branch
follow all of the instructions in the comments.
to test your work, from the integrated terminal, type tsnode types.ts — the Typescript will bark at you and spew error messages if you did anything wrong, or forgot anything.
once you finished everything and tsnode types.ts shows no errors, submit a MR so I can see your code and leave any comments for corrections.

Bash Variable Review Assignment

do (again) steps 2-12 of the CLI #1 assignment from week 8 — the pdf is here
then, do the Extra Credit from CLI #2 of that same week (which also deals with bash variables). Slack us with instructions on how to do your madlib.

← All homework