zeptobook

class Person {  
  static age = 25;
  static firstname = 'fname';
  static lname = 'lname';
  static city = 'jersey city';
  
}
console.log(Person.age);
console.log(Person.firstname);
console.log(Person.lname);

zeptobook

const p1 = new Promise((res, rej) => setTimeout(res, 1000));

const p2 = new Promise((res, rej) => setTimeout(rej, 1000));

Promise.allSettled([p1, p2]).then(data => console.log(data));

// [
//   Object { status: "fulfilled", value: undefined},
//   Object { status: "rejected", reason: undefined}
// ]

zeptobook

class Message {
  #message = "ZeptoBook"

  greet() { console.log(this.#message) }
}

const greeting = new Message()

greeting.greet() // ZeptoBook
console.log(greeting.#message) // Private name #message is not defined

zeptobook

if(condition) {
  const mathModule = await import('./dynamicModule.js');
  mathModule.sum(10, 20);
}

zeptobook

const bigInt = 1234567890123456789012345678901234567890n;

const bigIntFromNumber = BigInt(10); // same as 10n

zeptobook

const nullValue = null;
const emptyText = ""; // falsy
const someNumber = 42;

const valA = nullValue ?? "default for A";
const valB = emptyText ?? "default for B";
const valC = someNumber ?? 0;

console.log(valA); // "default for A"
console.log(valB); // "" (as the empty string is not null or undefined)

zeptobook

const foo = null ?? 'default string';
console.log(foo);
// expected output: "default string"

const baz = 0 ?? 42;
console.log(baz);
// expected output: 0

zeptobook

let func = () => {
  return 'function call'
}

console.log(func()) // function call

func = null

console.log(func()) // error: Uncaught TypeError: func is not a function

zeptobook

person =  null;

console.log(person?.[0]); // undefined
// or

person = ['adam', 'robert'];
console.log(person?.[2]); // undefined

zeptobook

person =  null;

console.log(person[0]); // error: Uncaught TypeError: Cannot read property '0' of null
// or

person = ['adam', 'robert'];
console.log(person[2]); // error: Uncaught TypeError: Cannot read property '0' of null