问使用regex和javascript使链接可点击，但不覆盖预先存在的链接？

EN

var text = [
        "http://www.example.com/page address at the begining then a well formated a tag take a look <a href='http://www.example.com/page'>here</a>.",
        " text in front http://www.example.com/page Please take a look <a href='http://www.example.com/page'>here</a>.",
        "  http less with get vars www.example.com/page?foo=bar Please take a look  <a href='http://www.example.com/page'>here</a>.",
        '<p>http://example.com/<br /><a href="http://example.com/123">http://example.com/123</a><br /><a href="http://Google.ca/">http://Google.ca/</a></p>'
    ] ,
    reg = /([\s>]|^)((?:http:\/\/)?(?:[a-z][\w-]+)+(?:\.[\w-]+)*(?:\.[a-z]{2,3})(?:[^ <]+))(?=[\s<]|$)/g,
    output = '';
    for(var key in text){
        $('body').append(
        '<div>'+
          text[key]
                .replace(reg, '$1<a href="$2">$2</a>')
                .replace(/(href=['"])(?!http:\/\/)/g, '$1http://')+
        '</pre>'
        );
    }