Compact JSON Schema

Write less code without losing functionality. Full type support is also included in flight ✈️

import { unfoldSchema } from 'compact-json-schema'

const schema = unfoldSchema({ name: "string", surname: "string?" })

Converts to

{
  type: "object",
  properties: {
    name: {
      type: "string"
    },
    surname: {
      type: "string"
    }
  },
  required: [ "name" ]
}

Using

There are 5 basic types, which are typed as a relevant string:

"string" | "boolean" | "number" | "integer" | "object" | "array"

Each type can also be undefined or nullable:

"string?"    // Undefined type
"string??"   // Nullable or undefined type

You have two ways to write the schema, full or shorthand:

const fullSchema = schema({ name: { type: "string" } })
const shortSchema = schema({ name: "string" })
// fullSchema is equal to shortSchema

The schema for objects can also be written in two ways:

const fullSchema = schema({ user: { type: "object", props: { name: "string" } } })
const shortSchema = schema({ user: { name: "string" } })
// fullSchema is equal to shortSchema

As you can guess, the full path also allows you to specify the necessary settings for validation, while the short path just uses the defaults.

Compact form for union types

You can use array of items for shorthand enum or oneOf types:

const body = schema({ name: [ "file" ], filename: "string" })
const body2 = schema({ name: [ "image" ], size: "number" })

const schema = unfoldSchema([ body, body2 ])

Schema converts to

{
  oneOf: [
    {
      type: "object",
      properties: { 
        name: { type: "string",  const: "file" },
        filename: { type: "string" }
      },
      required: [ "name", "filename" ]
    },
    {
      type: "object",
      properties: { 
        name: { type: "string",  const: "image" },
        size: { type: "number" }
      },
      required: [ "name", "size" ]
    }
  ]
}

What's up with the types?

Example fastify:

import { schema, sc, SchemaType, unfoldSchema } from 'compact-json-schema'

const params = schema({ itemId: "number" })
const body = schema({ name: "string", surname: "string?", features: { type: "array", items: "string" } })

fastify.post("/user/:userId", { schema: { params: unfoldSchema(params), body: unfoldSchema(body) } }, async (req) => {
  const { userId } = req.params as SchemaType<typeof params>      // typeof userId === "number"
  const userData = req.body as SchemaType<typeof body>  
  /*
    userData: {
      name: string
      surname: string | undefined
      features: Array<string>
    }
  */
})

About fastify integration

Since this library was intended more for use with the fastify framework, this package has a sc utility that allows you to abbreviate writing `{ schema: { params ... } } in your endpoints.

It works a little tricky, allowing you to write a minimum of code. It is based on the fact that in most cases schemas are needed for "params" and for "body". If you want to change a key, pass it as the last argument to sc.

It is applied as follows:

sc(schema({ userId: "number" })) -> { schema: { params: { type: "object", properties: { userId: { type: "number" } } } }}

sc(schema({ userId: "number" }, "query")) -> { schema: { querystring: { type: "object", properties: { userId: { type: "number" } } } }}

sc(schema({ userId: "number" }, { age: "number" })) -> { 
  schema: { 
    params: { type: "object", properties: { userId: { type: "number" } } },
    body: { type: "object", properties: { age: { type: "number" } } },
  }
}

sc(schema({ userId: "number" }, { age: "number" }), "query") -> { 
  schema: { 
    params: { type: "object", properties: { userId: { type: "number" } } },
    querystring: { type: "object", properties: { age: { type: "number" } } },
  }
}

Alternatively, you can pass an object to schema in which you specify the required parameters:

sc({ body: schema({ userId: "number" }) }) -> { schema: { body: { type: "object", properties: { userId: { type: "number" } } } }}

Fastify Type Provider

Fastify also gives you the option of specifying a TypeProvider so that the schema is applied automatically:

import { schema, sc, SchemaType, CompactJsonSchemaProvider } from 'compact-json-schema'

const params = schema({ itemId: "number" })
const body = schema({ name: "string", surname: "string?", features: { type: "array", items: "string" } })

const app = fastify().withTypeProvider<CompactJsonSchemaProvider>()

app.post("/user/:userId", sc({ params, body }), async (req) => {
  const { userId } = req.params         // typeof userId === "number"
  const userData = req.body
  /*
    userData: {
      name: string
      surname: string | undefined
      features: Array<string>
    }
  */
})

And there's a little bit of a hack if you want to propagate Schema Provider globally. To do this, add the code:

declare module 'fastify' {
  interface FastifyTypeProviderDefault {
    output: this['input'] extends SchemaItem? SchemaType<this['input']>: any,
  }
}