***자료형(Data Type)***
console . log () -> 개발자탭의 콘솔 탭에서 확인 가능함
<!DOCTYPE html >
<html lang = "ko" >
<head>
<meta charset = "UTF-8" >
<meta name = "viewport" content = "width=device-width, initial-scale=1.0" >
<title> Document </title>
<script>
//console.log("aaaaa");
document . write ( "TEXT : " + typeof ( "TEXT" ));
</script>
</head>
<body>
</body>
</html>
<!DOCTYPE html >
<html lang = "ko" >
<head>
<meta charset = "UTF-8" >
<meta name = "viewport" content = "width=device-width, initial-scale=1.0" >
<title> Document </title>
<script>
//console.log("aaaaa");
document . write ( "TEXT : " + typeof ( "TEXT" ));
document . write ( "<hr>" )
document . write ( "10 : " + typeof 10 );
document . write ( "<hr>" )
</script>
</head>
<body>
</body>
</html>
document . write ( "true : "
+ typeof true );
document . write ( "<hr>" )
var arr = [ "aa" , "bb" , "cc" ];
document . write ( "arr[0]" + arr [ 0 ]);
document . write ( "<hr>" )
document . write ( "arr[0]" + typeof arr );
document . write ( "<hr>" )
var now_date = new Date ();
document . write ( "Date : " + now_date );
document . write ( "<hr>" );
document . write ( "Date : " + typeof now_date );
*변수(variable)
<!DOCTYPE html >
<html lang = "ko" >
<head>
<meta charset = "UTF-8" >
<meta name = "viewport" content = "width=device-width, initial-scale=1.0" >
<title> 변수선언문 </title>
<script>
var a = 1 ;
a = 2 ; // 값을 바꾸는것 -> 재할당
var a = 3 ; // 재선언
let b = 1 ;
b = 2 ;
let b = 3 ; // SyntaxError
</script>
</head>
<body>
</body>
</html>
const c = 1 ;
// c = 2; //Type Error
const c = 3 ; //SyntaxError
const c ; (선언만 하면 값은 오류가남, 문법적 오류)
const c = 1 ; (값의 오류)
c = 2 ;
const c = [ "aa" , "bb" , "cc" ];
c = 2; ㄴ> 에러
c[0] = "dd";
c 자체를 바꾸는건 안되지만 c 자체가 갖고있는 배열값이나 객체값은 바꿀 수 있음
<!DOCTYPE html >
<html lang = "ko" >
<head>
<meta charset = "UTF-8" >
<meta name = "viewport" content = "width=device-width, initial-scale=1.0" >
<title> 지역변수/전역변수 </title>
<script>
var a = 1 ;
//document.write(a);
var a = 2 ;
//document.write(a);
function change_var (){
var a = 3 ;
}
document . write ( a );
</script>
</head>
<body>
</body>
</html>
function change_var (){
var a = 3 ;
}
document . write ( a );
<!DOCTYPE html >
<html lang = "ko" >
<head>
<meta charset = "UTF-8" >
<meta name = "viewport" content = "width=device-width, initial-scale=1.0" >
<title> 지역변수/전역변수 </title>
<script>
var a = 1 ;
//document.write(a);
var a = 2 ;
//document.write(a);
function change_var (){
a = 2 ;
document . write ( a + "//" ); //2
var a = 3 ;
document . write ( a + "::::" ); //3
}
change_var ();
document . write ( a );
//function안에서 만들어진 변수들은 function 안에서만 사용할 수 있다.
</script>
</head>
<body>
</body>
</html>
//function안에서 만들어진 변수들은 function 안에서만 사용할 수 있다. -> 지역 변수
