json-schema-proxy/index.js

const Ajv = require('ajv')


module.exports = (obj={}, inSchema, outSchema) => {
    if (!inSchema) throw new ReferenceError('input schema not defined')

    const inValidate  = (new Ajv()).compile(inSchema)
    let   outValidate;

    if (outSchema){
        outSchema                      = {...outSchema}
        outSchema.additionalProperties = false
        outValidate                    = (new Ajv()).compile(outSchema)
    }

    return new Proxy(obj, {
        get(obj, prop){
            if (outValidate && !outValidate(obj)){
                if (outValidate.errors.find(({instancePath}) => instancePath.slice(1).startsWith(prop)) ||
                    (outValidate.errors[0].keyword === 'additionalProperties' && outValidate.errors[0].params.additionalProperty === prop)){
                    return;
                }
            }
            return obj[prop]
        },
        set(obj, prop, value){
            const newObject = {...obj, [prop]: value}
            if (!inValidate(newObject)){
                throw new TypeError(JSON.stringify([inValidate.errors, prop, value], null, 4))
            }
            obj[prop] = value
        }
    })
}

const schema = {
    type: "object",
    properties: {
        foo: {type: "integer"},
        bar: {type: "string"}
    },
    required: ["foo"],
    additionalProperties: false
}

const outSchema = {
    type: "object",
    properties: {
        foo: {type: "integer"},
    },
    required: ["foo"],
    additionalProperties: false
}

let validated = module.exports({}, schema, outSchema)

validated.foo = 5;
validated.bar = "string";
console.log(validated.foo)
console.log(validated.bar)
console.log({...validated})
//validated.bar = 100500;