do{ var year1=parseInt(prompt("請輸入員工的入職年份")); if (isNaN(year1)) { alert("請輸入正確的年份"); }else if(year1<0){ alert("請輸入公元前年份"); }else if(year1.toString().length!=4){ alert("請輸入四位數字年份"); }else("請輸入員工入職年份"); break; }while( (isNaN(year1))||year1<0||(year1.toString().length!=4) );