<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title>Page Title</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<script>
window.onload = function() {
var len1 = getByClass('on', 'list');
alert(len1.length); // 结果等于2为正确
var len2 = getByClass('on');
alert(len2.length); // 结果等于3为正确
}
function getByClass(clsName, parent) {
//定义函数getByClass
var oP = parent ? document.getElementById(parent) : document;
//是一个判断语句,如果传入parent即parent存在,那么var op = document.getElementById(parent),不存在的话就是var op = document
var a = oP.getElementsByTagName('*');
var b = new Array();
for (var i = 0; i < a.length; i++) {
if (a[i].className == clsName) {
b.push(a[i]);
}
return b;
}
}
</script>
</head>
<body>
<ul id="list">
<li class="on">1</li>
<li class="select">2</li>
<li class="on">3</li>
<li>4</li>
</ul>
<p class="on">class为on的p标签</p>
</body>
</html>
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