I found this problem with serialization / deserialization of objects of type CircuitValue in snarky-js when arrayProp is involved, not sure if it is correct or not....

output.md

Running the version without arrayProp

[nodemon] starting `node --no-warnings --experimental-specifier-resolution=node --loader ts-node/esm try_circuit_serialization.ts`

* checking if JSONized objects match after parsing

{ a: '1', b: { value: '1' } }
{ a: '1', b: { value: '1' } }

* checking if after parsing the object retains field-based type

if hasn't crashed then ok...

and if we run with arrayProp

TypeError: o.toJSON is not a function
    at /Users/marek/Development/octa/prototype/transaction-data-repository/node_modules/snarkyjs/dist/server/index.js:3:4884
    at Array.forEach (<anonymous>)
    at Function.toJSON (/Users/marek/Development/octa/prototype/transaction-data-repository/node_modules/snarkyjs/dist/server/index.js:3:4859)
    at Bla.toJSON (/Users/marek/Development/octa/prototype/transaction-data-repository/node_modules/snarkyjs/dist/server/index.js:3:4411)
    at file:///Users/marek/Development/octa/prototype/transaction-data-repository/try_circuit_serialization_array.ts:42:44
[nodemon] app crashed - waiting for file changes before starting...

try_circuit_serialization.ts

import {
    Field,
    UInt64,
    Int64,
    CircuitValue,
    prop,
    isReady
} from 'snarkyjs';

await isReady;

class Bla extends CircuitValue {
    @prop a: Field;
    @prop b: UInt64;

    constructor(
        a: Field,
        b: UInt64
    ) {
        super();
        this.a = a;
        this.b = b;
    }
}

function castBla(inp: Bla | null): Bla {
    if (inp === null) {
        throw Error();
    }
    return inp;
}

console.log();
const bla = new Bla(
    new Field(1),
    new UInt64(new Field(1)));
const bla2: Bla = castBla(Bla.fromJSON(bla.toJSON()));

console.log("* checking if JSONized objects match after parsing")
console.log();

console.log(bla.toJSON());
console.log(bla2.toJSON());

console.log();
console.log("* checking if after parsing the object retains field-based type");
console.log();

const b1: UInt64 = bla.b;
const b2: UInt64 = bla2.b;

console.log("if hasn't crashed then ok...")
console.log();

try_circuit_serialization_array.ts

import {
    Field,
    UInt64,
    Int64,
    CircuitValue,
    prop,
    arrayProp,
    isReady
} from 'snarkyjs';

await isReady;

class Bla extends CircuitValue {
    @prop a: Field;
    @prop b: UInt64;
    @arrayProp(Int64, 5) vals: Int64[];

    constructor(
        a: Field,
        b: UInt64,
        vals: Int64[]
    ) {
        super();
        this.a = a;
        this.b = b;
        this.vals = vals;
    }
}

function castBla(inp: Bla | null): Bla {
    if (inp === null) {
        throw Error();
    }
    return inp;
}

console.log();
const bla = new Bla(
    new Field(1),
    new UInt64(new Field(1)),
    [new Int64(new Field(1)), new Int64(new Field(2)), new Int64(new Field(3))]);
const bla2: Bla = castBla(Bla.fromJSON(bla.toJSON()));

console.log("* checking if JSONized objects match after parsing")
console.log();

console.log(bla.toJSON());
console.log(bla2.toJSON());

console.log();
console.log("* checking if after parsing the object retains field-based type");
console.log();

const b1: UInt64 = bla.b;
const b2: UInt64 = bla2.b;

console.log("if hasn't crashed then ok...")
console.log();
console.log();
console.log();