Introduction to TypeScript

Frontend Development Consultancy
Tomas Corral Casas
Head of Frontend Technologies and Academy
Consulting for:

“ TypeScript is a
typed superset of JavaScript
that compiles to plain JavaScript. ”

TypeScript
Typing, scopes…
ES7
Decorators, async/await...
ES6
Classes, Modules...
ES5

Writing new code
Maintaining old code
Understanding code
5%25%70%
What does a developer spend time on?

Hungarian notation
Prefix Type Example
b Boolean var bIsVisible = true;
e DOM element var eHeader = document.getElementById('header');
f Function var fCallback = function () { … };
n Number var nSides = 4;
o Object var oPoint = new Point(200, 345);
a Array var aNames = ['Luke', 'Nick', 'David'];
s String var sUrl = 'http://www.google.com';
$ jQuery var $Header = $('#header);

Prefix Type Example
_ Private var _transformData = function (data) { … return result; }
Public var render = function () { … };
Protected
Scope

@private
@typedef
@param {string} color
@param {LACE_TYPES}
type
@public
@access
@protected
@package
@class
@constructor
@constant
@enum
JSDoc comments

Why types are so important?
Source
Code AST BytecodeParser
Bytecode
Generator
JIT Compiler
Garbage Collector
Core1
Interpreter
Machine
Code
Execution
Bytecode
Machine
Code
Additional
Cores

Basic Types
Union voidnull undefined
boolean number anynever
Tuplestring ArrayObject
Type assertions

Basic Types - Inferred
let month = 5;
let name = 'Mik';
let isVisible = false;
let cities = ['New York', 'Oxford', 'Valladolid'];
let person = {
firstName: 'Gerardo',
lastName: 'Abelardo'
};

Basic Types - Explicit
let month: number;
let name: string;
let isVisible: boolean;
let person: object;
let employee: any;
let cities: string[];
let customers: Array<any>;
let value: null;
let value2: undefined;
let value3: void;
let address: [string, number, string, string];

Basic Types
let someValue: any = "this is a string";
let strLength: number = (someValue as string).length;
let strLength2: number = (<string>someValue).length;
Type Assertions

Basic Types - Union
let area: string| undefined = property('area');
let element: HTMLElement | null = document.getElementById('passion');
let menu: Array<Link | Divider> = getMenu();

How TypeScript type-
checking works?

A.K.A “duck typing” or “structural
subtyping”.
Type-checking focuses on the shape
that values have.

Enums
String EnumsNumber Enums

Number Enums
enum WeatherType {
Sunny,
Cloudy,
Rainy,
Storm,
Frost,
Nightly
}
enum WeatherType {
Sunny = 1,
Cloudy = 2,
Rainy = 3,
Storm = 4,
Frost = 5,
Nightly = 6
}

Number Enums - Usage
class Weather {
getWeatherIcon(weatherType: WeatherType) {
switch (weatherType) {
case WeatherType.Sunny: return 'weather_sunny';
case WeatherType.Cloudy: return 'weather_cloudy';
case WeatherType.Rainy: return 'weather_rain';
case WeatherType.Storm: return 'weather_storm';
case WeatherType.Frost: return 'weather_frost';
case WeatherType.Nightly: return 'weather_nightly';
}
}
}

String Enums
enum WeatherType {
Sunny = 'weather_sunny',
Cloudy = 'weather_cloudy',
Rainy = 'weather_rain',
Storm = 'weather_storm',
Frost = 'weather_frost',
Nightly = 'weather_nightly',
}

Functions
Function Types Overloading

Function Types 1/3
function add(x: number, y: number): number {
return x + y;
}
function multiply(x: number, y: number): number {
return x * y;
}
let myAdd: (x: number, y: number) => number = add;
type twoOperandsType = (x: number, y: number) => number;
let myMultiply: twoOperandsType = multiply;

Function Types 2/3
function buildName(firstName: string, lastName?: string) {
if (lastName) { return `${firstName} ${lastName}`; }
else { return firstName; }
}
function buildAddress(street: string, postalCode: string = 'UNDEFINED') {
if (postalCode) { return `${street} ${postalCode}`; }
else { return street; }
}

Function Types 3/3
type buildStringOneOrMoreArguments = (x: string, y: string) => string;
const buildName1: buildStringOneOrMoreArguments = buildName;
const buildAddress1: buildStringOneOrMoreArguments = buildAddress;
function buildFamily(father: string, ...restOfFamily: string[]) {
return `${father} ${restOfFamily.join(" ")}`;
}

This
const mother = {
name: 'Maria',
sons: [
'Lucho',
'Mauro'
],
daughters: [
'Silvia',
'Romani'
],
getChildren(): string[] {
return this.sons.concat(this.daughters);
}
};
const father = {
name: 'Manolo',
sons: [
'Lucho',
'Mauro'
],
daughters: [
'Silvia',
'Romani'
],
getChildren(this: void) { // Avoid using this.
return this.sons.concat(this.daughters);
}
}

Arrow Function
let deck = {
suits: ["hearts", "spades", "clubs", "diamonds"],
cards: Array(52),
createCardPicker: function() {
return () => {
let pickedCard = Math.floor(Math.random() * 52);
let pickedSuit = Math.floor(pickedCard / 13);
return {
suit: this.suits[pickedSuit],
card: pickedCard % 13
};
}
}
};

Overloading
type propertiesObject = { [name: string]: any };
const properties: propertiesObject = {};
function property(propertyName: string, defaultValue: any ): any;
function property(propertyName: string): any | undefined;
function property(propertyName: string, defaultValue?: any) {
if (defaultValue) {
properties[propertyName] = defaultValue;
}
return properties[propertyName];
}

Interfaces
interface
implements

Interfaces
interface TreeLink {
type: string;
title: string;
url: string;
isCurrent: boolean;
preferences: any;
children: TreeLink[];
}
const treeLink: TreeLink = {
type: 'external',
title: 'Google',
url: 'http://www.google.nl',
isCurrent: false,
preferences: {
navIcon: 'accounts'
},
children: []
};

Implements
interface Flyable { fly: () => void }
interface Quackable { quack: () => void; }
class Duck implements Flyable, Quackable {
fly() { console.log('Fly, Fly, Fly'); }
quack() { console.log('Quack, Quack'); }
}
class Turkey implements Flyable {
fly() { console.log('Ufff!'); }
}

Classes
readonlypublic private protected
getters setters
static methods and properties
class abstractextends implements

Classes
class Animal {
name: string;
constructor(name: string) {
this.name = name;
}
}
class Animal {
constructor(
public name: string
) {}
}

Abstract Classes
abstract class Animal {
constructor(
public readonly name: string
) {}
abstract makeSound(): void;
abstract move(): void;
abstract getOffspring(): void;
}
abstract class Mammal extends Animal{
constructor(
public readonly name: string,
public readonly legs: number
) {
super(name);
}
}

Inheritance 1/3
class Whale extends Mammal {
constructor(){ super('Whale', 0); }
makeSound() { console.log('waaoaoooooooooooaoaoo'); }
move() { console.log('Swim, Swim, Swim, Swim, Swim!'); }
getOffspring() { console.log('Get birth a calf!'); }
}

Inheritance 2/3
class Dog extends Mammal {
constructor() { super('Dog', 4); }
makeSound() { console.log('Woof, Woof, Woof!'); }
move() { console.log('Walk, Walk, Walk!'); }
getOffspring() { console.log('Get birth a dozen puppies!'); }
}

Inheritance 3/3
class Platypus extends Mammal {
constructor() { super('Platypus', 4); }
makeSound() { console.log('hrrrrrrrrrrrh'); }
move() { console.log('Swim, Swim, Walk, Walk!'); }
getOffspring() { console.log('Put eggs and wait!'); }
}

Generics
Generic Types Generic Classes

Generics
function echo<T>(arg: T): T {
console.log(arg);
return arg;
}
echo('19th October');
echo<string>('Friday');
echo<number>(19);

Generic Types
function identity<T>(arg: T): T {
return arg;
}
let myIdentity: <T>(arg: T) => T = identity;
let myIdentity2: <U>(arg: U) => U = identity;

Generic Classes
class Operator<T> {
initialValue: T;
operation: (x: T, y: T) => T;
}
const numAdder = new Operator<number>();
numAdder.initValue = 10;
numAdder.operation = function(x, y) {
return this.initValue + x + y;
};
const strConc = new Operator<string>();
strConc.initValue = '';
strConc.operation = function (x, y) {
return `${this.initValue} ${x} ${y}`;
};

Modules and Namespaces
export import
Default exports Working with other libraries
Namespacing Multi-file namespace

Export
export class Cat {
constructor(private name: string, private legs: number){}
}
export default {
getCatInstance(name: string, legs: number) {
return new Cat(name, legs);
}
}

Import
import { Cat } from './Cat';
import { getCatInstance } from './utils';

Namespaces
export namespace Shapes {
export class Triangle { /* ... */ }
export class Square { /* ... */ }
}
import * as shapes from "./shapes";
let t = new shapes.Shapes.Triangle(); // shapes.Shapes?

Introduction to TypeScript

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