JS/TS validation of common restrictions (minimum, minLength, pattern, etc.)

[callumlocke]

Take this example JSON Schema, with integers restricted to certain ranges:

{
  "$id": "https://example.com/geographical-location.schema.json",
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "Longitude and Latitude Values",
  "description": "A geographical coordinate.",
  "required": [ "latitude", "longitude" ],
  "type": "object",
  "properties": {
    "latitude": {
      "type": "number",
      "minimum": -90,
      "maximum": 90
    },
    "longitude": {
      "type": "number",
      "minimum": -180,
      "maximum": 180
    }
  }
}

Currently, if you use quicktype to generate JavaScript or TypeScript from the above, the generated runtime validation functions only enforce that latitude and longitude are numbers.

It would be great if they could also enforce the minimum, maximum and other restrictions.

Here's a non-exhaustive list of restrictions I believe are not currently enforced by generated validation functions (gathered from this site):

• numeric restrictions:
  • minimum
  • maximum
  • exclusiveMinimum
  • exclusiveMaximum
  • multipleOf
  • integer (in JSON Schema this is actually a separate type, but could be treated as a restriction on number types in generated JS/TS code)
• string restrictions:
  • minLength
  • maxLength
  • pattern
• array restrictions:
  • maxItems
  • minItems
  • items when done as an array (doesn't seem to be enforced correctly)
• object restrictions:
  • additionalProperties
  • patternProperties - not sure how useful this is though

---

For the case of generated TypeScript definitions, it might make sense to generate opaque types to represent restricted types, as well as safe casting functions. Something like:

// helper
type Opaque<K, T> = T & { __opaque__: K };

export type Latitude = Opaque<'Latitude', number>;

export interface LatLon {
    latitude:  Latitude;
    longitude: Longitude;
}

// ...plus:
function castAsLatitude(num: number): Latitude {
    if (num < -90 || num > 90) invalidValue(num, 'Latitude');
    return num as Latitude;
}

[kdisneur]

Hi!

I just found this library because we would like to generate some Go code from our JSON-Schema. This feature is exactly what is missing from all the JSON-Schema -> Code converters we found.

I was wondering if you already planned to add this in your roadmap and if we could somehow help you to make this one happen. 🙂

Thanks

[jasonkolodziej]

Same here!!!!

[gpodila-disc]

+1 addition to what mentioned above, Im looking for unique values in array.