Mixing libraries shouldn't be a problem, although to justify adding another library I'd think there should be some greater benefit than just basic event syntax.
You can simplify the above sample posted by @Daniil even further if you wish. The syntax then becomes very similar.
Example
<%@ Page Language="C#" %>
<%@ Register Assembly="Ext.Net" Namespace="Ext.Net" TagPrefix="ext" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Ext.Net Example</title>
<script type="text/javascript">
var onReady = function () {
Ext.get("div1")
.hover(
function (e, el) {
Ext.get(this).addClass("div1-hover");
},
function (e, el) {
Ext.get(this).removeClass("div1-hover");
}
)
.on("click", function() {
Ext.Msg.alert("div", "I'm clicked");
});
};
</script>
<style type="text/css">
.div1 {
height : 50px;
width : 50px;
border : 2px solid;
}
.div1-hover {
background-color : red;
}
</style>
</head>
<body>
<form runat="server">
<ext:ResourceManager runat="server">
<Listeners>
<DocumentReady Handler="onReady();" />
</Listeners>
</ext:ResourceManager>
<div id="div1" class="div1"></div>
</form>
</body>
</html>