js为元素动态增加class样式

div{ border:1px solid #ccc; width:200px; height:200px;}

.a{ background:#900; }

.b{ font-size:30px; font-weight:bold;}

function addClass(elements, value)

{

if (!elements.className) {

elements.className = value;

}

else

{

newClass = elements.className;

newClass += " ";

newClass += value;

elements.className = newClass;

}

}

window.onload = function ()

{

var test = document.getElementById('test');

alert(test.className);

addClass(test, 'a b');

//addClass(test, 'b');

}

<div id="test">这里是测试层</div>