当我们注册一个QQ的时候，会看到一个三级年月日的联动菜单，下面简单介绍。
<!doctype html><html lang="en"> <head> <meta charset="UTF-8"> <meta name="Generator" content="EditPlus®"> <meta name="Author" content=""> <meta name="KeyWords" content=""> <meta name="Description" content=""> <title>Document</title> </head> <body> <form name=form1> <select name=YYYY onchange="YYYYMM(this.value)"> <option value="">年</option> </select> <select name=MM onchange="MMDD(this.value)"> <option value="">月</option> </select> <select name=DD> <option value="">日</option> </select> </form> </body><script language="javaScript"> //定义年、月、日方法函数window.onload = function(){ strYYYY = document.form1.YYYY.outerHTML; strMM = document.form1.MM.outerHTML; strDD = document.form1.DD.outerHTML; MonHead = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]; //先给年下拉框赋内容 var y = new Date().getFullYear(); var str = strYYYY.substring(0, strYYYY.length - 9); for (var i = (y-30); i < (y+30); i++) //以今年为准，前30年，后30年 { str += "<option value='" + i + "'> " + i + "</option>/r/n"; } document.form1.YYYY.outerHTML = str +"</select>"; //赋月份的下拉框 var str = strMM.substring(0, strMM.length - 9); for (var i = 1; i < 13; i++) { str += "<option value='" + i + "'> " + i + "</option>/r/n"; } document.form1.MM.outerHTML = str +"</select>"; document.form1.YYYY.value = y; document.form1.MM.value = new Date().getMonth() + 1; var n = MonHead[new Date().getMonth()]; if (new Date().getMonth() ==1 && IsPinYear(YYYYvalue)) n++; writeDay(n); //赋日期下拉框 document.form1.DD.value = new Date().getDate(); } function YYYYMM(str) //年发生变化时日期发生变化(主要是判断闰平年) { var MMvalue = document.form1.MM.options[document.form1.MM.selectedIndex].value; if (MMvalue == ""){DD.outerHTML = strDD; return;} var n = MonHead[MMvalue - 1]; if (MMvalue ==2 && IsPinYear(str)) n++; writeDay(n) } //月发生变化时日期联动 function MMDD(str) { var YYYYvalue = document.form1.YYYY.options[document.form1.YYYY.selectedIndex].value; if (str == ""){DD.outerHTML = strDD; return;} var n = MonHead[str - 1]; if (str ==2 && IsPinYear(YYYYvalue)) n++; writeDay(n) } //据条件写日期的下拉框 function writeDay(n) { var s = strDD.substring(0, strDD.length - 9); for (var i=1; i<(n+1); i++) s += "<option value='" + i + "'> " + i + "</option>/r/n"; document.form1.DD.outerHTML = s +"</select>"; } //判断是否闰平年function IsPinYear(year){ return(0 == year%4 && (year%100 !=0 || year%400 == 0)) } </script></html>
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