How to know if a URL is decoded/encoded?

There is a simple way to konw if a URL string is encoded.

Take the initial string and compare it with the result of decoding it. If the result is the same, the string is not encoded; if the result is different then it is encoded.

I had this issue with my urls and I used this functions:

function isEncoded(uri) {
  uri = uri || '';

  return uri !== decodeURIComponent(uri);
}

So now I can use isEncoded as the discriminant in a while loop (or with recursion) to know if I need to keep calling decodeURIComponent on the string:

function fullyDecodeURI(uri){

  while (isEncoded(uri)){
    uri = decodeURIComponent(uri);
  }

  return uri;
}

This solved the problem for me of decoding urls encoded multiple times. Hope this helps.