JavaScript

JavaScript JavaScript 2

JavaScript ECMAScript (JavaScript) JavaScript HTML DOM Node.js JavaScript

ECMAScript HTML Node.js Deno JavaScript

JavaScript JavaScript

• : SharedArrayBuffer
• : HTML JavaScript (FIFO)
• : (LIFO)

3

1 1

• (Similar-origin window agent) Window document.domain
• (Dedicated worker agent) DedicatedWorkerGlobalScope
• (Shared worker agent) SharedWorkerGlobalScope
• (Service worker agent) ServiceWorkerGlobalScope
• (Worklet agent) WorkletGlobalScope

1 iframe Node.js

[2 1 HTML 1 ]

1 (realm) JavaScript

• ArrayArray.prototype
• globalThis

WindowWorkerGlobalScopeWorkletGlobalScope iframe

Array.isArray() Error.isError() Array.prototype instanceof Array false

• • varletconstfunctionclass
  • #foo
  • this

function foo(b) {
  const a = 10;
  return a + b + 11;
}

function bar(x) {
  const y = 3;
  return foo(x * y);
}

const baz = bar(7); // 42  baz 

1. foobarbaz bar 7
2. bar 2 x y x * y foo
3. foo 3 b a a + b + 11
4. foo foo(x * y)
5. bar bar(7) baz

function* gen() {
  console.log(1);
  yield;
  console.log(2);
}

const g = gen();
g.next(); // logs 1
g.next(); // logs 2

gen() gen g g.next() gen gen yield g.next() gen

(proper tail call, PTC)

function f() {
  return g();
}

g g()

function factorial(n, acc = 1) {
  if (n <= 1) return acc;
  return factorial(n - 1, n * acc);
}

g() f PTC Safari (JavaScriptCore)

let f;
{
  let x = 10;
  f = () => x;
}
console.log(f()); // logs 10

1 JavaScript HTML

I/OHTML 2 HTML

C C

const promise = Promise.resolve();
let i = 0;
promise.then(() => {
  i += 1;
  console.log(i);
});
promise.then(() => {
  i += 1;
  console.log(i);
});

2 1 2 i += 1; console.log(i); i += 1; console.log(i); i += 1; i += 1; console.log(i); console.log(i);

1

JavaScript I/O IndexedDB fetch() then() setTimeout()

API alert() XHR

2

• Window
• Window A A iframe Window
• Window Window
• Window

• Window
• Window
• Window A A iframe Window A
• 2 Window 2 Window

HTML

postMessage() SharedArrayBuffer 2 SharedArrayBuffer Atomics

2 JavaScript

ECMAScript

• API

• 1 API 2

• Event loops - HTML standard
• What is the Event Loop? - Node.js