TypeScript learning notes. From zero to hero.
1. Array, Tuple, Union, Enum // Basic Types let id: number = 5 //Add type after variable, separated by colon let company: string = 'Traversy Media' let isPublished: boolean = true let x: any = 'Hello' //any type variable can hold any type of data let ids: number[] = [1, 2, 3, 4, 5] //Variable-length array; different from traditional static language int a[4]; let arr: any[] = [1, true, 'Hello'] //any array, can mix various values // Tuple let person: [number, string, boolean] = [1, 'Brad', true] //Tuple: array with known number of elements and types; element types need not be the same. // Tuple Array let employees: [number, string][] //Array where each element is a tuple employee = [ [1, 'Brad'], [2, 'John'], [3, 'Jill'], ] // Union let pid: string | number //Union /* Below is C language union - a variable that can store several different types of data union data{ int n; char ch; double f; }; */ pid = '22' // Enum enum Direction1 { Up = 1, Down, Left, Right, } enum Direction2 { Up = 'Up', Down = 'Down', Left = 'Left', Right = 'Right', } 2. Map // Definition type MapType = { [id: string]: string; } // Instantiation const map: MapType = {}; map['a'] = 'b'; map['c'] = 'd'; // Deletion delete map['c']; // Enumeration for (let i in map) { console.log(map[i]); } // Get array containing all keys console.log(Object.keys(map)); // Another implementation using Record const map: Record<string, string> = {}; map['a'] = 'b'; map['c'] = 'd'; 3. Object // Objects type User = { id: number name: string } const user: User = { id: 1, name: 'John', } // Type Assertion - type casting let cid: any = 1 // let customerId = <number>cid Casting from any to number let customerId = cid as number 4. Function // Functions function addNum(x: number, y: number): number { return x + y } // Void function log(message: string | number): void { console.log(message) } 5. Interface, Class // Interfaces interface UserInterface { readonly id: number name: string age?: number } const user1: UserInterface = { id: 1, name: 'John', } interface MathFunc { (x: number, y: number): number } const add: MathFunc = (x: number, y: number): number => x + y const sub: MathFunc = (x: number, y: number): number => x - y interface PersonInterface { id: number name: string register(): string } // Classes class Person implements PersonInterface { id: number name: string constructor(id: number, name: string) { this.id = id this.name = name } register() { return `${this.name} is now registered` } } const brad = new Person(1, 'Brad Traversy') const mike = new Person(2, 'Mike Jordan') // Subclasses class Employee extends Person { position: string constructor(id: number, name: string, position: string) { super(id, name) this.position = position } } const emp = new Employee(3, 'Shawn', 'Developer') 6. Generics // Generics => Similar to C++ templates function getArray<T>(items: T[]): T[] { return new Array().concat(items) } let numArray = getArray<number>([1, 2, 3, 4]) let strArray = getArray<string>(['brad', 'John', 'Jill']) strArray.push(1) // Throws error 7. FAQ 7.1. type alias or interface https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#differences-between-type-aliases-and-interfaces
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