John Borges johnborges

JS Memory Leaks - Common Sources

addEventListener. This is the most common one. Call removeEventListener to clean it up.
setTimeout / setInterval. If you create a recurring timer (e.g. to run every 30 seconds), then you need to clean it up with clearTimeout or clearInterval. (setTimeout can leak if it’s used like setInterval – i.e., scheduling a new setTimeout inside of the setTimeout callback.)
IntersectionObserver, ResizeObserver, MutationObserver, etc. These new-ish APIs are very convenient, but they are also likely to leak. If you create one inside of a component, and it’s attached to a globally-available element, then you need to call disconnect() to clean them up. (Note that DOM nodes which are garbage-collected will have their listeners and observers garbage-collected as well.

String to Number

my_string = "123";
console.log(+my_string);
// 123

my_string = "amazing";
console.log(+my_string);
// NaN

Constructor

// This creates a new empty Object
var newObject = {};

// This creates a new empty Object
var newObject = Object.create(Object.prototype);

var newObject = new Object();

Because the JSON grammar is much simpler than JavaScript’s grammar, JSON can be parsed more efficiently than JavaScript. This knowledge can be applied to improve start-up performance for web apps that ship large JSON-like configuration object literals (such as inline Redux stores).

const data = { foo: 42, bar: 1337 }; // 🐌
const data = JSON.parse('{"foo":42,"bar":1337}'); // 🚀

7 Tricky JavaScript Interview Questions

Accidental Global

function foo() {
  let a;
  window.b = 0;
  a = window.b;
  a++;
  return a;

	rm -rf ~/Library/Caches/CocoaPods
	rm -rf Pods
	rm -rf ~/Library/Developer/Xcode/DerivedData
	pod deintegrate
	pod setup
	pod install

	const controller = new AbortController();
	const { signal } = controller;

	fetch("http://localhost:8000", { signal }).then(response => {
	console.log(`Request 1 is complete!`);
	}).catch(e => {
	console.warn(`Fetch 1 error: ${e.message}`);
	});

	fetch("http://localhost:8000", { signal }).then(response => {

	// simplified createStore function
	const createStore = (reducer) => {
	let listeners = [];
	let currentState = reducer(undefined, {});
	return {
	getState: () => currentState,
	dispatch: (action) => {
	currentState = reducer(currentState, action);
	listeners.forEach((listener) => {
	listener();

	const obj = {
	...condition && { prop: value },
	};