Primitive Type(원시 타입)

  • string
  • number
  • biginit
  • boolean
  • undefined
  • symboll
  • null
  • 재할당 하더라도, 처음 할당했던 값이 바뀌지 않음

Reference Type(참조 타입)

  • function
  • array
  • object
  • 재할당하면, 모든 것이 자동적으로 다 바꿔버림
  • save inside ‘heap’


  • determines the accessibility of variables
  • JS receive own scope once function was created, which is lexical scope(check who is its outer scope)
  • can put function inside function

Local Scope vs. Global Scope

Local Scope

  • ‘Local Variable’(지역변수) has higher priority than global variable and cannot use it outside function

Global Scope

  • ‘Global Variable’(전역변수) can access everywhere

Function Scope vs. Block Scope


  • starts and end with curly bracket { }

var vs. let

  • var: gets its own scope (old way)
  • connects with window object
  • let: only works inside block scope

Global Variable(전역변수) and Window object(윈도우객체)

  • will connect to function that is assigned at global scope and var variable
  • do not declare too much in global scope!

No Declaration(선언없이 초기화된 전역변수)

  • do not use variable without assignment
  • if it does, it becomes global variable(전역변수)
  • In order to avoid error, use ‘use strict’




Consistency achieves everything

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Joo Hee Paige Kim

Joo Hee Paige Kim

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