/**
 * @param 
 * @arrange (512.笔记) jb51.cc
 **/
<style type="text/css">
.newDiv {
    font-weight: bold;
}
</style>

<script>
function clk(event) {
    var parent = document.getElementById("parent");
    //改变className
    var child0 = document.createElement("div");
    child0.innerHTML = "child0";
    child0.className = "newDiv";
    parent.appendChild(child0);
    //改变<a href="http://jb51.cc/" title="css">css</a>Text
    var child1 = document.createElement("div");
    child1.innerHTML = "child1";
    child1.style.<a href="http://jb51.cc/" title="css">css</a>Text = "font-weight: bold";
    parent.appendChild(child1);
    //改变直接样式
    var child2 = document.createElement("div");
    child2.innerHTML = "child2";
    child2.style.fontWeight = "bold";
    parent.appendChild(child2);
}
</script>

/**
 * @param 
 * @arrange (512.笔记) jb51.cc
 **/
<input type="button" value="click" onclick="clk(event);"/>
<div id="parent">
    <div>child</div>
</div>