Javascript calculated property which is serializable

JS-getter-with-proxy

// Typescript accessor fields are not part of the serilization process
// A Proxy object serves the purpose ina very elegant way
// Other alternative would be to use `Object.defineProperty`

class Q {
    constructor(init: number) {
        var proxy = new Proxy(this, {
            get: (target, prop, receiver) => {
                if (prop === "msg") {
                    return `Number is ${this.value}`;
                }
                return Reflect.get(target, prop, receiver);
            },
        });

        this.value = init;

        return proxy; 
    }

    value: number;
    readonly msg: string|undefined = undefined; // must have an explicit value; if not, the property will not exist in the object 
}

var q = new Q(42);
var s = JSON.stringify(q);
console.log(s); // msg is part of the serialized object
console.log(q);