Should JSON include null values [closed]

Question

I'm creating an API that returns results as JSON. Is there a current best practice for whether we should include keys in the result when the value is null? For example:

{     "title":"Foo Bar",     "author":"Joe Blow",     "isbn":null } 

or

{     "title":"Foo Bar",     "author":"Joe Blow" } 

Since the second is smaller I am leaning towards this style, but I'm not sure if there is a preferred style or not. From a client perspective it seems like both styles would be functionally equivalent. Any pros or cons to each?

Answer 1

I am a fan of always including null explicitly as that carries meaning. While omitting a property leaves ambiguity.

As long as your protocol with the server is agreed upon any of the above can work, but if you pass nulls from the server I believe that makes your APIs more flexible later.

Should also mention that javascript's hasOwnProperty function gives you further insight.

/* if true object DOES contain the property with *some* value */ if( objectFromJSON.hasOwnProperty( "propertyName" ) )  /* if true object DOES contain the property and it has been set to null */ if( jsonObject.propertyName === null )  /* if true object either DOES NOT contain the property    OR    object DOES contain the property and it has been set to undefined */ if( jsonObject.propertyName === undefined ) 

Answer 2

The second will save a small amount on bandwidth, but if that were a concern you would also use indexed arrays instead of filling the JSON with keys. Clearly, ["Foo Bar","Joe Blow"] is much shorter than what you have now.

In terms of usability, I don't think it makes any difference. In both cases, if(json.isbn) will skip to the else. There is usually no need to distinguish between null (no value) and undefined (no given value).