Types for knowledge sharing

ts_intro.ts

// BASIC
const language: string = 'JavaScript';
const age: number = '33'; // Error
const amount = 55;
const price = '5';
const discount = false;
const total = price * amount; // Error
price - discount; // Error

// Reassigning
let skills: string;
skills = 'JavaScript';
skills = 'Java';
skills = true; // Error

// Literal types
let attempts: 3 = 3;
attempts  = 4; // Error
attempts = null; // depends on compilator configuration

let fruit: string;
let bananaFruit: 'banana' = 'banana';

fruit = bananaFruit; // Ok
bananaFruit = fruit; // Error

//any + unknown
let animal: unknown;
animal = 'Dog';
animal = 5;
animal.toString(); // Error



// Functions
function getAge(name: string): number {
    // ......
    return Math.ceil(Math.random() * 100);
}

function getDrakulaAge(): never {
    throw Error(`Drakula age couldn't be defined`);
}

function setAge(name: string, age: number): void {

}

function isAdult(age: number): boolean {
    return age >= 18;
}

isAdult(getAge('USER_NAME'));
isAdult(getDrakulaAge());
isAdult(setAge('Drakula', 20));