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function mapValues(obj, fn) {
  return Object.keys(obj).reduce((result, key) => {
    result[key] = fn(obj[key], key);
    return result;
  }, {});
}

function pick(obj, fn) {
  return Object.keys(obj).reduce((result, key) => {
    if (fn(obj[key])) {

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Простые задачи на яваскрипт

Пропустить теорию и перейти прямо к задачам

Ссылка на учебник: http://learn.javascript.ru

Сразу расскажу про несколько особенностей яваскрипта, о которых может быть не написано (или мало написано) в учебниках, но которые стоит понимать:

Версии яваскрипта

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1. Что покажут эти два alert()?

var foo = 'Hello';

(function() {
  var bar = ' World';
  console.log(foo + bar);
})();

console.log(foo + bar);

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Hidden classes in JavaScript and Inline Caching

Knowing how internals work is always a good. Pretty much for everything. Cars, trains, computers, you name it. It gives you an insight on what happens under the hood. You also act/react differently based on this knowledge.

As you might have guessed, it’s also true for web development. Knowledge of CSS transitions allows you to achieve better performance and not to use JavaScript in most cases. Knowledge of V8 internals allows you to write more performant JavaScript code. So let’s talk about V8 a little.

A little about V8

V8 is a JavaScript engine built by Google. Firefox built SpiderMonkey, Opera built Carakan and Microsoft built Chakra. One very important difference between V8 and other JavaScript engines is that V8 doesn’t generate any intermediate code. It compiles JavaScr

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section .text
global _start

_start:
  xor eax, eax              ; init eax 0
  xor ebx, ebx              ; init ebx 0
  xor esi, esi              ; init esi 0
  jmp _socket               ; jmp to _socket

_socket_call: