const nums = [1, 2, 3];
const obj = { a: 1, b: 2, c: 3 };

function process(...args) {
  const [first, ...rest] = args;
  const { a, ...others } = obj;
  return { first, rest, a, others };
}

const result = process(...nums);
console.log(result.first);
console.log(result.rest.length);
console.log(result.others.b);
console.log(Object.keys(result.others).join(''));
console.log(result.a === nums[0]);

let obj = { name: 'Sarah', age: 25 };
let weakMap = new WeakMap();
let map = new Map();

weakMap.set(obj, 'weak reference');
map.set(obj, 'strong reference');

console.log(weakMap.has(obj));
console.log(map.has(obj));

obj = null;

console.log(weakMap.has(null));
console.log(map.has(null));
console.log(map.size);