Cannot validate optional+null circulare fields about runtypes

[Deco]

I just tried my own suggestion and it worked.

const {Boolean, Number, String, Literal, Array, Record, Union, Optional, Null, Lazy} = require("runtypes");

const Person = Lazy(() =>
    Record({
        name: String,
        partner: Optional(Person.Or(Null)),
    })
);

try {
    const jsonBlob1 = JSON.parse(`{ "name": "Bob", "partner": { "name": "Janet" }}`);
    Person.check(jsonBlob1);
    console.info("Scenario 1 succeeded!");
} catch (e) {
    console.error(`Scenario 1 failed: ${e}`);
}

try {
    const jsonBlob2 = JSON.parse(`{ "name": "Bob", "partner": null }`);
    Person.check(jsonBlob2);
    console.info("Scenario 2 succeeded!");
} catch (e) {
    console.error(`Scenario 2 failed: ${e}`);
}

try {
    const jsonBlob3 = JSON.parse(`{ "name": "Bob" }`);
    Person.check(jsonBlob3);
    console.info("Scenario 3 succeeded!");
} catch (e) {
    console.error(`Scenario 3 failed: ${e}`);
}

Scenario 1 succeeded!
Scenario 2 succeeded!
Scenario 3 succeeded!

The order of operations here is a bit of a gotcha. Perhaps even warning worthy?

[JakeShirley]

Excellent, thanks for the quick responses! This makes total sense, if your example @yuhr isn't in the README/wiki, I'd suggest adding it. It made it very clear!

[Deco]

Try switching the order of optional and Or Null, and let us know how it goes:
So instead of Optional(Person).Or(Null),, try Optional(Person.Or(Null)).

[yuhr]

Yeah, if you want mark your property to be optional (i.e. able to be absent), Optional must be the outmost wrapper of your property. Optional(runtype) is no different from Union(runtype, Undefined) in any places other than direct children of a Record. If you wrote partner: Optional(Person).Or(Null) it's just equivalent to partner: Union(Optional(Person), Null) and then partner: Union(Union(Person, Undefined), Null), so it means the property must be present and be Person | undefined | null.

To summarize the correspondence of the runtypes to the TS's types:

• Record({ property: Optional(String).Or(Null) }): { property: string | null | undefined }
• Record({ property: Optional(String.Or(Null)) }): { property?: string | null | undefined }