TypeScript: Powtórka z JavaScript

Equality · 1 min

// Equality
1 == "1"; /*?*/
1 === "1"; /*?*/

"" == "0"; /*?*/
"" == 0; /*?*/
"" === "0"; /*?*/
"" === 0; /*?*/

References · 2 min

// References 
let x = 10;
let y = x;
x; /*?*/
y; /*?*/
y = 2;
x; /*?*/

let obj = {};
let refObj = obj;

obj.id = 123;
console.log(refObj.id);

let data = {};
let ref = data;
let moreData = {};

data === ref; /*?*/
data === moreData; /*?*/

null vs undefined · 3 min

// Null vs undefined
null == undefined; /*?*/
let somevar; // undefined
somevar != null; /*?*/

// root level undefined
typeof globalVar !== 'undefined'; /*?*/

this · 4 min

// this
function sayYo() { return `Yo! ${this}` }
sayYo(); /*?*/

const myObj = { welcome: sayYo };
myObj.welcome(); /*?*/

closure · 5 min

// closure
function outer() {
  const outsideScopeVar = 'out of the box';
  function inner() { return outsideScopeVar; }
  
  return inner;
}

const getInner = outer();
getInner(); /*?*/

truthy falsy values · 6 min

// truthy & falsy values
if (1) {
  console.log('ok! 😁');
}
if (0) {
  console.log('not ok! 🙁');
}

// bang bang
!!''; /*?*/
!!0; /*?*/
!!NaN; /*?*/
!!null; /*?*/
!!undefined; /*?*/
!!{}; /*?*/
!![]; /*?*/