TypeScriptAndFunctionalProgramming.js

// ====================================== *********** ==============================
// Function Currying
// ====================================== *********** ==============================

function multiply(a, b, c) {
    return a * b * c;
}

function multiply(a) {
    return (b) => {
        return (c) => {
            return a * b * c
        }
    }
}

console.log(multiply(1)(2)(3)) // 6





let finalMultipleFn = multiply(1)(2);

calculateSomething(finalMultipleFn)

async function calculateSomething(fn) {
    let x = await ajaxCall();
    return fn(x)
};
// Discounted price example

// let getDiscountedPrice = (percentDiscount) => {
//     return (price) => (price) - (price * percentDiscount) / 100;
// }

// let getPriceWith10PercentDiscount = getDiscountedPrice(10);
// let getPriceWith20PercentDiscount = getDiscountedPrice(20);

// let price1 = getPriceWith10PercentDiscount(100)
// let price2 = getPriceWith20PercentDiscount(100)

// console.log(price1);
// console.log(price2);

// ====================================== *********** ==============================
// Basic types in TS
// ====================================== *********** ==============================

const color: string = "blue";
const isDone: boolean = false;

const list1: number[] = [1, 2, 3];
const list2: Array<number> = [1, 2, 3];

const notSure: any = 4;

const multiType: string | number | boolean = true;

// ******** Functions  ************ //

function foo(message) {
  return message === "Hello";
}

function bar(message: string): boolean {
  return message === "Hello";
}

bar(25);

let baz = (message: number | string): string => "xyz"

// ====================================== *********** ==============================
// Classes in TS
// ====================================== *********** ==============================
class Animal {
  private name: string;
  protected color: string; // Accessible in child class

  constructor(theName: string, theColor: string) {
    this.name = theName;
    this.color = theColor;
  }

  private sayHi() {
    console.log("Hi");
  }
}


const animal = new Animal("Cat", "White");

console.log(animal.name); // Error: 'name' is private;
console.log(animal.color); // Error: 'color' is protected; with nice information on hover

animal.sayHi();


// ====================================== *********** ==============================
// Interfaces in TS
// ====================================== *********** ==============================

// Interface example ********************

interface IsroInterface {
  vehicleName?: string;
  readonly launchDate: Date;
  isLauncherReady: () => boolean; // no body just defination
}

class Isro implements IsroInterface {
  vehicleName: string;
  readonly launchDate: Date;
  constructor() {
    this.launchDate = new Date();
    this.vehicleName = "chandrayan";
  }

  changeLaunchDate() {
    this.launchDate = new Date("2019-11-23");
  }

  // isLauncherReady() {
  //   return true;
  // }
}

// Interface extending and combining ********************

interface Circle {
  radius: number;
}

interface Shape extends Circle {
  area: number;
  calc: (length: number) => number
}


let obj: Shape = {
  radius: 10,
  area: 100,
  calc: length => length * length
};

// Merging interface

interface Person {
  name: string;

}

interface Person {
  age: number;

}

interface Person {
  zipCode: number;
}


let obj: Person = {
  name: "Vivek",
  zipCode: 411058,
  age: 26,
};



// ====================================== *********** ==============================
// Generics in TS
// ====================================== *********** ==============================

function identity(arg: string): string {
  return arg;
}

function identity<T>(arg: T): T {  // T is placeholder
  return arg;
}

// Multiple generic variables *****************

let output1 = identity<number>(10); // If not provided 'number' as value of T here
// T will be 10 then 
let output2 = identity("myString"); // In this case T will be "myString" not string 

// On hover it shows T's value.
// Suggest properties on return type of it.


function identityNew<T, U>(arg1: T, arg2: U): [T, U] {
  const list: [T, U] = [arg1, arg2];
  return list;
}

identityNew("xyz", 123);

// Generic Classes  *****************

class GenericNumber<T, U> {
  numbValue: T;

  identity(x: U): U {
    return x;
  }
}

let myGenericNumber = new GenericNumber<number, string>();
// We can also have generic interfaces


// Generic Interfaces  *****************

// interface Identities<V, W> {
//   id1: V;
//   id2: W;
// }

// class ABC implements Identities<string, number> {
//   id1: string = "abc";
//   id2: number = 20;
// }


// ====================================== *********** ==============================
// Decorators in TS
// ====================================== *********** ==============================

// ******************************** //
// Can change class or function body, constructor code or methods on classes;
// ******************************** //



// *********** Replace Class **************

const replaceClass = (originalConstructor) => {
  debugger;
  return class newPet {
    constructor() { console.log("In new PET class") }
    printMe() {
      console.log("New printMe method")
    }
  }
}

@replaceClass
class Pet {
  constructor(name: string, age: number) { }
  printMe() {
    console.log("Orignal printMe method")
  }
}

console.log(Pet)



// *********** Change Class **************
const replaceClassMethod = (originalConstructor) => {
  originalConstructor.prototype.printMe = function printMe() {
    console.log("New printMe method")
  }
  return originalConstructor;
}

@replaceClassMethod
class Pet {
  constructor(name: string, age: number) { }
  printMe() {
    console.log("Orignal printMe method")
  }
}

const pet = new Pet("Azor", 12)
pet.printMe()

// *********** Method decorator **************

class Greeter {

  @greetWithNewMessage
  greet() {
    return "Hello";
  }
}

function greetWithNewMessage(target: any, propertyKey: string, descriptor: PropertyDescriptor) {
  debugger;
  descriptor.value = function () {
    return "How are you";
  };
}

const greeter = new Greeter();

console.log(greeter.greet())


// Use of decorators.

class CRUD {
    get() { }
    post() { }
 
    @admin
    delete() { }
 
    @owner
    put() { }
}

// One can decorate class properties as well as method parameters.
// ====================================== *********** ==============================
// Why TypeScript - IntelliSense, Error detection
// ====================================== *********** ==============================

interface IsroInterface {
  vehicleName: string;
  launchDate: Date;
  launch: () => void;
  isLauncherReady: () => boolean;
}

class Isro implements IsroInterface {
  vehicleName: string;
  launchDate: Date;
  constructor() {
    this.launchDate = new Date();
    this.vehicleName = "chandrayan";
  }

  launch() {
    if (this.launchDate === "2019-11-23") {
      console.log("Launch rocket");
    }
  }

  isLauncherReady() {
    return "yes";
  }
}

const isro = new Isro()

isro.

// Shows intelliscence, Function details  (In real case it might be in different file), Errors