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complete ts chapter - 3
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‎README.md‎

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|:-------:|:-------:|
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| 1: Getting started with TypeScript | [Readme](/chapters/1/readme.md) |
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| 2: Why and when to use TypeScript | [Readme](/chapters/2/readme.md) |
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| 3: TypeScript Core Types | [Readme]() |
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| 3: TypeScript Core Types | [Readme](/chapters/3/readme.md) |
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| 4: Arrays | [Readme]() |
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| 5: Enums | [Readme]() |
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| 6: Functions | [Readme]() |

‎chapters/1/readme.md‎

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# Getting started with Node.js
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# Getting started with TypeScript
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| **Topic** | **Code** |
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|:---------:|:--------:|

‎chapters/2/readme.md‎

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# npm
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# Why and when to use TypeScript
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| **Topic** | **Code** |
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|:---------:|:--------:|

‎chapters/3/codes/3.1/app.ts‎

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/*
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String literal types allow you to specify the exact value a string can have.
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*/
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let myFavoritePet: "dog";
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// console.log(myFavoritePet); // undefined
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/*
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myFavoritePet = "rock";
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console.log(myFavoritePet);
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// Error: Type '"rock"' is not assignable to type '"dog"'.
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*/
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myFavoritePet = "dog";
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//console.log(myFavoritePet); // dog
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// Together with Type Aliases and Union Types you get a enum-like behavior.
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type Species = "cat" | "dog" | "bird";
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// They works well for User-Defined Type Guards.
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interface Pet {
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species: Species;
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name: String;
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eat();
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sleep();
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}
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interface Cat extends Pet {
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species: "cat";
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}
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interface Dog extends Pet {
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species: "dog";
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walk();
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}
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interface Bird extends Pet {
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species: "bird";
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sing();
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}
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/*
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Error: Interface 'Rock' incorrectly extends interface 'Pet'. Types of property 'species' are
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incompatible. Type '"rock"' is not assignable to type '"cat" | "dog" | "bird"'. Type '"rock"' is not
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assignable to type '"bird"'.
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interface Rock extends Pet {
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type: "rock";
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}
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*/
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// String Literal Types can be used to distinguish overloads.
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function buyPet(pet :Species, name: String) : Pet;
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function buyPet(pet :"cat", name: String) : Cat;
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function buyPet(pet :"dog", name: String) : Dog;
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function buyPet(pet :"bird", name: String) : Bird;
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function buyPet(pet :Species, name: String) : Pet {
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if(pet === "cat") {
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return {
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species: "cat",
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name: name,
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eat: function () {
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console.log(`${this.name} eats.`);
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},
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walk: function () {
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console.log(`${this.name} walks.`);
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},
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sleep: function () {
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console.log(`${this.name} sleeps.`);
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}
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} as Cat;
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} else if(pet === "dog") {
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return {
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species: "dog",
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name: name,
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eat: function () {
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console.log(`${this.name} eats.`);
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},
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walk: function () {
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console.log(`${this.name} walks.`);
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},
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sleep: function () {
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console.log(`${this.name} sleeps.`);
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}
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} as Dog;
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} else if(pet === "bird") {
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return {
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species: "bird",
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name: name,
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eat: function () {
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console.log(`${this.name} eats.`);
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},
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walk: function () {
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console.log(`${this.name} walks.`);
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},
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sleep: function () {
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console.log(`${this.name} sleeps.`);
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},
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sing: function () {
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console.log(`${this.name} sings.`);
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}
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} as Bird;
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} else {
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throw `Sorry we do not have a ${pet}. Would you like to buy a dog?`;
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}
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};
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function petIsCat(pet: Pet): pet is Cat {
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return pet.species === "cat";
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}
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function petIsDog(pet: Pet): pet is Dog {
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return pet.species === "dog";
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}
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function petIsBird(pet: Pet): pet is Bird {
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return pet.species === "bird";
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}
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function playWithPet(pet: Pet){
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console.log(`Hey ${pet.name}, lets play.`);
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if(petIsCat(pet)) {
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// pet is now from type Cat (pet: Cat)
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pet.eat();
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pet.sleep();
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/*
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// Error: Type '"bird"' is not assignable to type '"cat"'.
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// pet.type = "bird";
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// Error: Property 'sing' does not exist on type 'Cat'.
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// pet.sing();
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*/
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} else if(petIsDog(pet)) {
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// pet is now from type Dog (pet: Dog)
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pet.eat();
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pet.walk();
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pet.sleep();
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} else if(petIsBird(pet)) {
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// pet is now from type Bird (pet: Bird)
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pet.eat();
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pet.sing();
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pet.sleep();
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} else {
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throw "An unknown pet. Did you buy a rock?";
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}
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}
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let dog = buyPet(myFavoritePet /* "dog" as defined above */, "Dog-Rocky");
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let bird = buyPet(myFavoritePet /* "bird" as defined above */, "Bird-Rocky");
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let cat = buyPet(myFavoritePet /* "cat" as defined above */, "Cat-Rocky");
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playWithPet(dog);
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console.log('-----------------\n');
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playWithPet(bird);
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console.log('-----------------\n');
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playWithPet(cat);
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console.log('-----------------\n');
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/*
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Hey Dog-Rocky, lets play.
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Dog-Rocky eats.
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Dog-Rocky walks.
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Dog-Rocky sleeps.
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-----------------
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Hey Bird-Rocky, lets play.
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Bird-Rocky eats.
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Bird-Rocky walks.
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Bird-Rocky sleeps.
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-----------------
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Hey Cat-Rocky, lets play.
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Cat-Rocky eats.
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Cat-Rocky walks.
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Cat-Rocky sleeps.
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-----------------
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*/

‎chapters/3/codes/3.10/app.ts‎

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// An array of values:
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let threePigs: number[] = [1, 2, 3];
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let genericStringArray: Array<string> = ['first', '2nd', '3rd'];
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console.log(threePigs); // [ 1, 2, 3 ]
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console.log(genericStringArray); // [ 'first', '2nd', '3rd' ]

‎chapters/3/codes/3.11/app.ts‎

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// A type to name a set of numeric values:
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// Number values default to 0:
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enum Day { Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday };
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let bestDay: Day = Day.Saturday;
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console.log(Day);
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/*
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{
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'0': 'Monday',
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'1': 'Tuesday',
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'2': 'Wednesday',
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'3': 'Thursday',
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'4': 'Friday',
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'5': 'Saturday',
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'6': 'Sunday',
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Monday: 0,
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Tuesday: 1,
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Wednesday: 2,
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Thursday: 3,
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Friday: 4,
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Saturday: 5,
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Sunday: 6
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}
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*/
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console.log(bestDay); // 5
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//Set a default starting number:
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enum TenPlus { Ten = 10, Eleven, Twelve }
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console.log(TenPlus);
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/*
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{
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'10': 'Ten',
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'11': 'Eleven',
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'12': 'Twelve',
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Ten: 10,
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Eleven: 11,
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Twelve: 12
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}
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*/
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//or assign values:
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enum MyOddSet { Three = 3, Five = 5, Seven = 7, Nine = 9 }
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console.log(MyOddSet);
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/*
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{
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'3': 'Three',
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'5': 'Five',
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'7': 'Seven',
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'9': 'Nine',
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Three: 3,
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Five: 5,
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Seven: 7,
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Nine: 9
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}
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*/

‎chapters/3/codes/3.12/app.ts‎

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// When unsure of a type, any is available:
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let anything: any = 'I am a string';
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console.log(anything); // I am a string
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anything = 5; // but now I am the number 5
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console.log(anything); // 5

‎chapters/3/codes/3.13/app.ts‎

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/*
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If you have no type at all, commonly used for functions that do not
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return anything:
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*/
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function log(): void {
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console.log('I return nothing');
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}
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log(); // I return nothing
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// void types Can only be assigned null or undefined .

‎chapters/3/codes/3.2/app.ts‎

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// Array type with known and possibly different types:
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let day: [number, string];
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day = [0, 'Monday'];
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console.log(day) // valid [ 0, 'Monday' ]
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/*
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day = ['zero', 'Monday']; // invalid: 'zero' is not numeric
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Type 'string' is not assignable to type 'number'.ts(2322)
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*/
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console.log(day[0]); // 0
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console.log(day[1]); // Monday
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day[1] = 'Saturday'; // valid: [ 0, 'Saturday' ]
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/*
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day[2] = 'Sunday';
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// Tuple type '[number, string]' of length '2' has no element at index '2'.
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day[3] = false;
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// invalid: must be union type of 'number | string'
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*/
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console.log(day)

‎chapters/3/codes/3.3/app.ts‎

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/*
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A boolean represents the most basic datatype in TypeScript, with the purpose of
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assigning true/false values.
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*/
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// set with initial value (either true or false)
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let isTrue: boolean = true;
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console.log(isTrue); // true
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// defaults to 'undefined', when not explicitly set
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let unsetBool: boolean;
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console.log(unsetBool); // undefined
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// can also be set to 'null' as well
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let nullableBool: boolean = null;
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console.log(nullableBool); // null

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