regex - Check if a string starts with http using Javascript

Question

I've been searching all over for an answer to this and all of the answers I've found haven't been in JavaScript.

I need a way, in javascript, to check if a string starts with http, https, or ftp. If it doesn't start with one of those I need to prepend the string with http://. indexOf won't work for me I don't think as I need either http, https or ftp. Also I don't want something like google.com/?q=http://google.com to trigger that as being valid as it doesn't start with an http whereas indexOf would trigger that as being true (if I'm not entirely mistaken).

The closest PHP regex I've found is this:

function addhttp($url) {
   if (!preg_match("~^(?:f|ht)tps?://~i", $url)) {
      $url = "http://" . $url;
   }
   return $url;
}

Source: How to add http if its not exists in the url

I just don't know how to convert that to javascript. Any help would be greatly appreciated.

question from:https://stackoverflow.com/questions/11300906/check-if-a-string-starts-with-http-using-javascript

Answer 1

export const getValidUrl = (url = "") => {
    let newUrl = window.decodeURIComponent(url);
    newUrl = newUrl.trim().replace(/s/g, "");

    if(/^(://)/.test(newUrl)){
        return `http${newUrl}`;
    }
    if(!/^(f|ht)tps?:///i.test(newUrl)){
        return `http://${newUrl}`;
    }

    return newUrl;
};

Tests:

expect(getValidUrl('https://www.test.com')).toBe('https://www.test.com');
expect(getValidUrl('http://www.test.com')).toBe('http://www.test.com');
expect(getValidUrl('    http   :    /  /  www.test.com')).toBe('http://www.test.com');
expect(getValidUrl('ftp://www.test.com')).toBe('ftp://www.test.com');
expect(getValidUrl('www.test.com')).toBe('http://www.test.com');
expect(getValidUrl('://www.test.com')).toBe('http://www.test.com');
expect(getValidUrl('http%3A%2F%2Fwww.test.com')).toBe('http://www.test.com');
expect(getValidUrl('www    .  test.com')).toBe('http://www.test.com');