Version: 2020sp

Lecture 9

Final Project due May 6 7:59pm

Lecture Video

Lecture Slides


To deploy your web application means to put it on a Web server so others can access it via the internet. We will deploy frontend on Firebase and backend on Heroku.

Frontend Deployment#

To deploy to Firebase enter the following commands into terminal:

yarn global add firebase-tools
yarn build
firebase login
firebase init
<answer the questions>
firebase deploy

yarn build will create a build directory containing a production build of your application.

firebase login will prompt you to log in by opening up a web browser if you're not already signed it.

firebase init will ask you the following questions:

  1. Which Firebase CLI features do you want to set up for this folder? Select Hosting.
  2. Associate with a Firebase project. Select your Firebase project
  3. What do you want as your public directory? build
  4. Configure as a single-page app (rewrite all urls to /index.html)? Yes
  5. Overwrite index.html? No

Running firebase deploy will push your build assets to Firebase remote server and give you a URL to your live Firebase app site! Now you can share this site and access it over the internet.

Backend Deployment#

We will deploy backend on Heroku because deploying on Firebase is much more involved

yarn global add heroku
git init
git add .
git commit -m "COMMIT MESSAGE"
heroku login
heroku create <optional project name>
git push heroku master
(optional) heroku open

You can then use the url generated as your backend endpoint in your frontend code.


One of the best parts about Firebase is you can use Sign in with Google/Facebook/GitHub/etc! This way you don't have to deal with usernames and passwords yourself!

We did a Live Coding Demo here based on the Songs example from last week. I will include the files changed here.

To handle authentication we made a wrapper component Authenticated to handle all Authentication:

import React, { useState } from 'react';
import 'firebase/auth';
import * as firebase from 'firebase/app';
import FirebaseAuth from 'react-firebaseui/FirebaseAuth';
import { useEffect } from 'react';
const firebaseConfig = {}; // put firebase config in here
export default (props) => {
const [user, setUser] = useState(null);
const uiConfig = {
signInFlow: 'popup',
signInOptions: [firebase.auth.GoogleAuthProvider.PROVIDER_ID],
function onAuthStateChange() {
return firebase.auth().onAuthStateChanged((user) => {
useEffect(() => onAuthStateChange(), []);
return (
{user && props.children}
{!user && (
<FirebaseAuth uiConfig={uiConfig} firebaseAuth={firebase.auth()} />

We then wrap our whole SongList app in Authenticated.

import React from 'react';
import logo from './logo.svg';
import './App.css';
import SongList from './SongList';
import Authenticated from './Authenticated';
function App() {
return (
<div className="App">
<SongList />
export default App;

If the user is logged in, SongList will show. Otherwise they will be asked to log in.

We then deployed this app on Firebase for the frontend and Heroku for the backend. Refer to the commands above.


TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. Superset means TypeScript has everything in JavaScript and more. (Built by Microsoft!)

JavaScript Types#

JavaScript has 6 primitive types:

  • Boolean
  • String
  • Number
  • Symbol
  • undefined
  • BigInt

All JavaScript values are those 6 primitive types or a:

  • object
  • function (JavaScript is functional!)
  • null

How are types used?#

In JavaScript we had:

let str = 'Hello, trends';
let num = 42;
let truth = true;
const someFunc = (x, s, b) => {
// do some operations...
return x;

Notice we don't have any types here! JavaScript is weakly typed.

let str: string = 'Hello, trends';
let num: number = 42;
let truth: boolean = false;
const someFunc = (x: number, s: string, b: boolean): number => {
// do some operations...
return x;

TypeScript allows us to add type information!

Why TypeScript?#

JavaScript code can be ambiguous. We had the function:

const someFunc = (x, s, b) => {
// do some operations...
return x;

What are x, s, b? What should I pass in for those? What should I expect returned?

Adding the TypeScript types makes this code self-documenting:

const someFunc = (x: number, s: string, b: boolean): number => {
// do some operations...
return x;

JavaScript variables can also change type which can be undesirable, unexpected, and error-prone.

let str = 'Hello, trends';
let num = 42;
let truth = true;
str = 13;

None of these variables have to be any specific type! I can have str be a string and then a number.

In the end, we want to use TypeScript because it is:

  • Easier to read
  • Easier and faster to implement
  • Easier to refactor
  • Less buggy

TypeScript Types#

Basic Syntax:

let <var_name>: <type> = <something>;

We can also use const but again no var.

Basic Types#

// Boolean
let isDone: boolean = false;
// Number can be decimal, or in any base!
let decimal: number = 4.2;
let binary: number = 0b1010;
let hex: number = 0xf00d;
// String
let lang: string = 'typescript';
let templateStr: string = `We love ${lang}`;
// Boolean
let isDone: boolean = false;
// Number can be decimal, or in any base!
let decimal: number = 4.2;
let binary: number = 0b1010;
let hex: number = 0xf00d;
// String
let lang: string = 'typescript';
let templateStr: string = `We love ${lang}`;


Any is a wildcard and it can be anything. any places no restrictions on type.

// Any: can be anything!
let notSure: any = 4;
notSure = 'maybe a string instead';
notSure = false; // okay, definitely a boolean

If you were to use any everywhere though you might as well just use JavaScript

let anyList: any[] = [4, 'maybe a string', false];

But it can be useful in specifying collections of items of different types!


Functions can have types too!

// un-typed
const myFunc = (x, y) => x + y;
// typed
const myFunc = (x: number, y: number): number => x + y;

myFunc has type (x: number, y: number): number.

TypeScript can do some limited type inference so if you leave out the return type number, TypeScript can infer it since we are just adding two numbers which can only produce a number. If TypeScript can't infer the type, it defaults as any.

We can also have optional parameters:

const introduce = (name: string, github?: string): string => {
return github
? `Hi, I'm ${name}. Checkout my GitHub @${github}`
: `Hi, I'm ${name}. I don't have a GitHub.`;

github? designates github as an optional parameter that defaults to undefined.

Literal Types#

Literal Types are types that can be a literal set of possibilities that you specify. TypeScript allows number and string literal types:

String Literal Types#
// String literal type
type TrafficLightColors = 'red' | 'green' | 'yellow';

Any variable with TrafficLightColors type can only take on values "red", "green", "yellow".

let light1: TrafficLightColors = 'red';
light1 = 'blue'; // TypeError
Numeric Literal Types#
// Numeric literal type
type DiceRoll = 1 | 2 | 3 | 4 | 5 | 6;
const rollDice = (): DiceRoll => {
// ...

Union Types#

With union types, a variable can be of one type or another type.

const union: number | string = 5; // number
const union2: number | string = 'hello'; // string
type TrafficLightColors = 'red' | 'green' | 'yellow';
type PrimaryColors = 'red' | 'green' | 'blue';
// "red" | "green" | "yellow" | "blue"
type union = PrimaryColors | TrafficLightColors;

Intersection Types#

With union types, a variable must be of one type and another type.

// Intersection Type
type TrafficLightColors = 'red' | 'green' | 'yellow';
type PrimaryColors = 'red' | 'green' | 'blue';
type intersect = PrimaryColors & TrafficLightColors; // "red" | "green"

Type Inference#

Type inference is determining type information without being told explicitly. TypeScript has limited type inference capabilities. If it can't infer the type the default is any.

Sometimes type inference is easy:

// TypeScript can infer these types
let isDone = false; // boolean
let decimal = 4.2; // number
let lang = 'typescript'; // string

Other times it involves some more advanced reasoning:

const whatType = (a, b, c) => (a(b + 1) === true ? b : c);

What are the types of a, b, c and what is the return type?

First b should be a number because we are adding 1 to it. Knowing b should be a number, a should then be a function taking in a number and returning a boolean. Finally, this function returns either b or c and b is already a number so c must also be number. Thus the return type is number.

We expect the following types:

a: number => boolean
b: number
c: number
return: number

In reality TypeScript infers the following:

a: any
b: any
c: any
return: any

Add TypeScript to React!#

You can learn how to add TypeScript to your Create React App application here.