小编use*_*251的帖子

var range = document.createRange();
var root_node = document.getElementById("test");

range.setStart(root_node,0);
range.setEnd(root_node,3);

var newNode = document.createElement("b");

range.surroundContents(newNode);

<div id="test">
    <p>h</p>ello    
</div>