function styleOnload(node, callback) {
// for IE6-9 and Opera
if (node.attachEvent) {
node.attachEvent('onload', callback)
// NOTICE:
// 1. "onload" will be fired in IE6-9 when the file is 404, but in
// this situation, Opera does nothing, so fallback to timeout.
// 2. "onerror" doesn't fire in any browsers!
}
}
更详细的判断：http://www.jbxue.com/article/15944.html
