Je retiens:

Virer les false ou équivalents dans un array

 array.filter(boolean)

Mélanger des objets

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",
}
*/

Récupérer la query string

 // Assuming "?post=1234&action=edit"
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()); // "?post=1234&action=edit"
console.log(urlParams.append('active', '1')); // "?post=1234&action=edit&active=1"

Récuperer l'URL absolue

var getAbsoluteUrl = (function() {
    var a;
    return function(url) {
        if(!a) a = document.createElement('a');
        a.href = url;
        return a.href;
    };
})();
// Usage
getAbsoluteUrl('/something'); // https://davidwalsh.name/something