Scope
Scope determines the accessibility (visibility) of variables.
JavaScript has 3 types of scope:
Block scope
efore ES6 (2015), JavaScript had only Global Scope and Function Scope.
ES6 introduced two important new JavaScript keywords: let and const.
These two keywords provide Block Scope in JavaScript.
Variables declared inside a { } block cannot be accessed from outside the block:
Variables declared with the var keyword can NOT have block scope.
Variables declared inside a { } block can be accessed from outside the block.
Function scope
JavaScript has function scope: Each function creates a new scope.
Variables defined inside a function are not accessible (visible) from outside the function.
Variables declared with var, let and const are quite similar when declared inside a function.
Global scope
A variable declared outside a function, becomes GLOBAL.
Variables declared Globally (outside any function) have Global Scope.
Global variables can be accessed from anywhere in a JavaScript program.
Variables declared with var, let and const are quite similar when declared outside a block.
Reference : https://www.w3schools.com/js/js_scope.asp
Javascript Primitive type vs Reference type (원시자료형 vs 참조자료형)
원시타입(7)
변수에 값(value) 이 담김
String
Number
Boolean
Bigint
undefined
Symbol
null
값이 절때 변하지않는 불변성을 갖고있기때문에 때문에 재할당 시 기존 값이 변하는것 처럼 보일지 몰라도 사실 새로운 메모리에 재할당한 값이 저장되고 변수가 가리키는 메모리(주소)가 달라졌을 뿐
참조타입
변수에 할당할 때는 변수에 값이 아닌 주소를 저장
원시타입을 제외한 나머지(배열,객체,함수 대표적)
원시타입과 가장 큰 차이점은 변수의 크기가 동적으로 변함
