If user enters his text in the text box and saves it and again what's to add some more text he can edit that text and save it if required.

Firstly if user enters that text with some links I, detected them and converted any hyperlinks to linkify in new tab. Secondly if user wants to add some more text and links he clicks on edit and add them and save it at this time I must ignore the links that already hyperlinked with anchor button

Please help and advice

For example:

what = "<span>In the task system, is there a way to automatically have any site / page URL or image URL be hyperlinked in a new window?</span><br><br><span>So If I type or copy http://www.stackoverflow.com/&nbsp; for example anywhere in the description, in any of the internal messages or messages to clients, it automatically is a hyperlink in a new window.</span><br><a href="http://www.stackoverflow.com/">http://www.stackoverflow.com/</a><br>    <br><span>Or if I input an image URL anywhere in support description, internal messages or messages to cleints, it automatically is a hyperlink in a new window:</span><br> <span>https://static.doubleclick.net/viewad/4327673/1-728x90.jpg</span><br><br><a href="https://static.doubleclick.net/viewad/4327673/1-728x90.jpg">https://static.doubleclick.net/viewad/4327673/1-728x90.jpg</a><br><br><br><span>This would save us a lot time in task building, reviewing and creating messages.</span>



Test URL's
        http://www.stackoverflow.com/
        http://stackoverflow.com/
        https://stackoverflow.com/
        www.stackoverflow.com
        //stackoverflow.com/
        <a href='http://stackoverflow.com/'>http://stackoverflow.com/</a>";

I've tried this code

function Linkify(what) {
    str = what; out = ""; url = ""; i = 0;
    do {
        url = str.match(/((https?:\/\/)?([a-z\-]+\.)*[\-\w]+(\.[a-z]{2,4})+(\/[\w\_\-\?\=\&\.]*)*(?![a-z]))/i);
        if(url!=null) {
            // get href value
            href = url[0];
            if(href.substr(0,7)!="http://") href = "http://"+href;

            // where the match occured
            where = str.indexOf(url[0]);

            // add it to the output
            out += str.substr(0,where);

            // link it
            out += '<a href="'+href+'" target="_blank">'+url[0]+'</a>';

            // prepare str for next round
            str = str.substr((where+url[0].length));
        } else {
            out += str;
            str = "";
        }
    } while(str.length>0);
    return out;
}

Please help Thanks.