perf

// Old way
if (user && user.address && user.address.city) {
  console.log(user.address.city);
}

// Modern way with Optional Chaining
console.log(user?.address?.city);

// Nullish Coalescing
const userName = user.name ?? 'Guest';


// Using an object
const obj = {};
obj['key1'] = 'value1';
delete obj['key1'];

// Using a Map
const map = new Map();
map.set('key1', 'value1');
map.delete('key1');


const arr = [1, 2, 3, 4, 5];

// Using forEach
arr.forEach(num => console.log(num));

// Using for loop
for (let i = 0; i < arr.length; i++) {
  console.log(arr[i]);
}


// Dynamic import
import('path/to/module').then(module => {
  module.default();
});


const list = document.getElementById('list');

// Inefficient
list.style.backgroundColor = 'blue';
list.style.color = 'white';

// Efficient
list.style.cssText = 'background-color: blue; color: white;';