Individually validating key/value pairs in a type

[kasperbb]

I'm looking for a way to validate single key/value pairs in a Type similar to how a compiled Scope works. I can't use a scope for this because the key/value pair could be optional. From my understanding, a key can be optional in a type, but there is no way to validate just that single key/value. You can validate single keys for scopes, but no optional keys exist.

class Example<T extends Scope> {
  constructor(private schema: T) {}

  // This is essentially how I want to validate the data, key by key
  private validate<K extends keyof T['infer']>(key: K, value: unknown) {
    return this.schema.compile()[key](value);
  }
}

// Inferred as "{ foo: string; 'bar?': string }"
const scopeExample= scope({
  foo: 'string',
  'bar?': 'string'
});

// Inferred as "{ foo: string; bar?: string | undefined }"
const typeExample = type({
  foo: 'string',
  'bar?': 'string'
});

const types = scopeExample.compile();
types.foo(data);
types.bar(data); // types['bar?'](data)

[ssalbdivad]

At some point, we'll add the ability to index in to types like "myType['foo']" (like TS) and probably additionally using the JS dot notation i.e. myType.foo.

I've created an issue to track that here:

#831

For now, I think the easiest thing to do would just be to have a list of "optional" aliases passed to Example. When validating an alias from that list, you could check if the input was undefined before passing it to the scope validator and allow it.

Let me know if that feels like an acceptable intermediate solution!