//NaN / unde / null / 0 = false console.log("1"); if(NaN){ // NaN == false console.log("2"); } console.log("3"); //1,3 //multi-if var n = prompt("정수값을 입력하시오") n = parseInt(n); if(n>=90 ){ console.log("A학점"); }else if(n>=80){ console.log("B학점"); }else if(n>=70){ console.log("C학점"); }else{ console.log("F학점"); } //switch var n = "홍2"; switch(n){ case "홍2": console.log("홍2"); break; case "홍3": conso..