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来源：7-9 JS对表单元素进行设置5

ByteDancer07

2020-01-24 14:37:24

index.js

function show1() {
	// body...
	var year = document.getElementById("year");
	var month = document.getElementById("month");
	var day = document.getElementById("day")

	var date = new Date();
	ymd(year,1999,date.getFullYear());
	ymd(month,1,12);
	ymd(day,1,31);

	var n = year.length;
	year.selectedIndex = Math.round(n/2);

}

function ymd(obj,start,end) {
	// body...
	for (var i =start;i<=end;i++) {
		obj.options.add(new Option(i,i));
	}
}


function changeYMD() {
	var month = document.getElementById("month");
	var day = document.getElementById("day");

	var m = month.value;

	if (m==4||m==6|m==9||m==11) {
		day.options.remove(day.length);
	}else if (m==2) {
		var year = document.getElementById("year");
		var y = year.value;

		
		if((y%4==0&&y%100!=0)||(y%4==0&&y%100==0)){
			for (var i = day.length-1; i>day.length-3;i--) {
				day.options.remove(i)
			}
		}else{
			for (var i = day.length-1; i>day.length-4;i--) {
				day.options.remove(i)
			}
		}
	}

}

html

<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<title>日历联动</title>
	<script type="text/javascript" src="testJs.js"></script>
</head>
<body onload="show1()">
	<form>
		<select name="year" id="year" onchange="changeYMD()">年</select>
		<select name="month" id="month" onchange="changeYMD()">月</select>
		<select name="day" id="day" >日</select>

	</form>

</body>
</html>

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