javascript check if null from json

In your example, photo.caption is null, so your code breaks on the photo.caption.text call, before the check is done.

var caption;

if(photo.caption != null) { // Covers 'undefined' as well
  caption = photo.caption.text;
} else {
  caption = "meh";
}

In my case i use the JSON.stringify to check I have received {} (null) response from the REST server:

 if (JSON.stringify(response.data)=='{}') {
      //the response is null
 }
 else {
      //the response of JSON is not null
 }

It works fine for me to check if the response is null or not.