JavaScript

• High-level, Prototype-based / Object-oriented, Multi-paradigm, Interpreted or Just-in-time Compiled, Dynamic, Single-threaded, Garbage-collected, First-class finctions, Event Loop Concurrency Model

High-level

• JS, Python : 메모리 관리가 필요 없음
• 그러므로 C언어처럼 빠르지 않음

Garbage Collection

• automatically removes old, unused memory from the computer memory in order not to clog it up with unnecessary stuff.
• we don't need to clean the memory manually.

Interpreted or just-in-time compiled

• machine code : 0 and 1
• Human-readable code -> JS translates it (compiling and interpreting happens inside JS Engine)

Multi-paradigm

• paradigm : an approach and mindset of structuring code, which will direct your coding style and technique.
• 패러다임의 종류 : Procedural Programming(organizing the code in a linear way with some functions between), Object-oriented programming(OOP), Functional Programming(FP)
• Imperative vs Declarative
• JS does everything. very versatile.

Prototype-based Object oriented

• EX. array : there is prototype of an array and the array we coded inherits methods from prototype and also is built from it. .... (ex. Array.prototype.push .. )

First-class Functions

• In a language with first-class functions, functions are simply treated as variables. We can pass them into other functions, and return them from functions.

const closeModal = () => {
	modal.classList.add("hidden");
    overlay.classList.add("hidden");
}

overlay.addEventListener("click", closeModal);
// 여기서 closeModal - passing a function into another functions as an argument : First-class Functions

Dynamic

• Dynamically-typed language. EX. let x = 23; x = 'yonneki';
• 데이터 타입을 정하지 않고 적어도 결정되고 그 뒤에 변수를 재할당하면 데이터 타입이 자동적으로 바뀐다. 예를 들어 자바와 같은 언어는 이를 허용하지 않는다.
• 이게 좋은지 나쁜지에 대한 의견은 분분하지만 어쨌든 자바스크립트는 이렇게 작동한다.

Single-threaded

• Concurrency Model : how the JS engine handles multiple tasks happening at the same time.
• We need concurrency model because JS runs in one single thread. so it can do one thing at a time.
• Thread is where our code is actually executed in a machine's processor.

Non-blocking Event Loop

• What if we have long-running tasks like fetching data from a remote server? Sounds like it would block the single-thread. How ever we want non-blocking behavior.
• By using an event loop : takes long running tasks, executes them in the 'background', and puts them back in the main thread once they are finished.
• In a nutshell, JavaScript is non-blocking event loop concurrency model with a single thread.