You can define a method that changes the url to something, and then replace your string and finally put the urls where they were before
    String.prototype.replaceStr = function (reg, strOrCallBack) {
        var str = this;
        var links = [];
        var found = true;
        while(found) {
            found = false;
            str = str.replace(/(https?:\/\/[^\s]+)/g, function(url) {
                links.push(url);
                found = true;
                return "(--" + (links.length-1) + "--)";
             });
        }
        str = str.replace(reg, strOrCallBack);
        return links.reduce(function (result, item, index) {
            return result.replace("(--" +  index + "--)", item);
        }, str);
    }
You can have on your string as many urls as you want and all the urls will stay the same after calling the method replaceStr
var somestr = "Welcome to stack overflow --> http://stackoverflow.com";
var replaced = somestr.replaceStr(/too/g, "at").replaceStr(/o/g, "0");
// "Welc0me t0 stack 0verfl0w --> http://stackoverflow.com"