• JS

/* 
    3. constants
    값이 변경 될 수 없는 값.
    favor immutable data type
    - security, 
    - thread safety, 
    - reduce human mistakes
*/
const maxNum = 5;
const dayOfyear = 365;

/*
    4. Variable types
    primitive, single item : number, string, boolean, null, undefined, symbol
    object, box container
    function, first-class function
*/
const max = function aa() {
  20;
};