Undefined array values seem to bypass validation

[from-the-river-to-the-sea]

Hi there!

This may be related to #116.

I have a simple schema that just checks if all items in a given array are strings. However, undefined values seem to pass this validation check, which is undesired. Example code can be found here: https://runkit.com/57ec9a7a8b6a9f1400abb925/5854116ee921e7001333f496

Is this a problem with my schema, or a problem with the generated validator function?

Thanks,
Alex

[LinusU]

Hmm, this is an interesting one 🤔

undefined isn't a type in JSON so it's not immediately clear exactly how this should be handled...

I think that right now we are handling undefined as "no value" which is why it passes.

This has some more implications though, what would we expect the following to give?

const schema = {
  type: 'object',
  properties: {
    a: { type: 'string' }
  }
}

const data = {
  a: undefined
}

Since the a property is optional, I'm not sure that this should give an error 🤔

Any input is welcome :)

[from-the-river-to-the-sea]

For me, this particular problem resulted in some interesting effects.

On the client, I was capturing some property of an array of DOM elements. There was a typo in my code, resulting in me just capturing an array full of undefined. This resulting array passed client-side validation, even though the intent of my schema was to ensure all items in the array are strings.

The array was then JSON serialized, sent across the wire, and received by my server. Some time later, my server would re-validate the data and unexpectedly fail. This is because undefined is serialized as null by JSON.stringify.

I often use JSON schemas in this manner to ensure that my code is doing the right thing, but in this case it doesn't seem to be able to offer me protection.

[LinusU]

Hmm, if JSON.stringify treats undefined as null, we should probably to the same here 👍