这将做你想要的，而不需要支持任何膨胀的库，如jQuery。

This will do what you want, without needing the support of any bloated libraries like jQuery.

var my_elem = document.getElementById('my_id');

var span = document.createElement('span');
    span.innerHTML = '*';
    span.className = 'asterisk';

my_elem.parentNode.insertBefore(span, my_elem);