Javascript / RegExp：隐式断言导致“无效组”错误

Uncaught SyntaxError: Invalid regular expression: /(?<=\\#\\!\\/)([^\\/]+)/: Invalid group

var url = window.location.toString();

url ==

// lookbehind to only match the segment after the hash-bang.

var regex = /(?<=\\#\\!\\/)([^\\/]+)/i; 
console.log(\'test this url: \', url, \'we found this match: \', url.match( regex ) );

write-stuff

<script>
var regex = /\\#\\!\\/([^\\/]+)/;
var url = \"http://my.domain.com/index.php/#!/write-stuff/something-else\";
var match = regex.exec(url);
alert(match[1]);
</script>