Check if a JavaScript string is a URL

Question

Is there a way in JavaScript to check if a string is a URL?

RegExes are excluded because the URL is most likely written like stackoverflow; that is to s

Answer 1

(I don't have reps to comment on ValidURL example; hence post this as an answer.)

While use of protocol relative URLs is not encouraged (The Protocol-relative URL), they do get employed sometimes. To validate such an URL with a regular expression the protocol part could be optional, e.g.:

function isValidURL(str) {
    var pattern = new RegExp('^((https?:)?\\/\\/)?'+ // protocol
        '(?:\\S+(?::\\S*)?@)?' + // authentication
        '((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|'+ // domain name
        '((\\d{1,3}\\.){3}\\d{1,3}))'+ // OR ip (v4) address
        '(\\:\\d+)?(\\/[-a-z\\d%_.~+]*)*'+ // port and path
        '(\\?[;&a-z\\d%_.~+=-]*)?'+ // query string
        '(\\#[-a-z\\d_]*)?$','i'); // fragment locater
    if (!pattern.test(str)) {
        return false;
    } else {
        return true;
    }
}

As others noted, regular expression does not seem to be the best suited approach for validating URLs, though.