var j = [...new Set([1, 2, 3, 4, 4])]
 [1, 2, 3, 4]

let res = [1,2,3,4,0,undefined,null,false,''].filter(Boolean);
 1,2,3,4

let dict = Object.create(null);

// dict.__proto__ === "undefined"
// No object properties exist until you add them

const person = { name: 'David Walsh', gender: 'Male' };
const tools = { computer: 'Mac', editor: 'Atom' };
const attributes = { handsomeness: 'Extreme', hair: 'Brown', eyes: 'Blue' };

const summary = {...person, ...tools, ...attributes};
/*
Object {
 "computer": "Mac",
 "editor": "Atom",
 "eyes": "Blue",
 "gender": "Male",
 "hair": "Brown",
 "handsomeness": "Extreme",
 "name": "David Walsh",
}
*/

const isRequired = () => { throw new Error('param is required'); };

const hello = (name = isRequired()) => { console.log(`hello ${name}`) };

// This will throw an error because no name is provided
hello();

// This will also throw an error
hello(undefined);

// These are good!
hello(null);
hello('David');

const obj = { x: 1 };

// Grabs obj.x as { x }
const { x } = obj;

// Grabs obj.x as { otherName }
const { x: otherName } = obj;

// Assuming ""

var urlParams = new URLSearchParams(window.location.search);

console.log(urlParams.has('post')); // true
console.log(urlParams.get('action')); // "edit"
console.log(urlParams.getAll('action')); // ["edit"]
console.log(urlParams.toString()); // ""
console.log(urlParams.append('active', '1')); // ""