Virtualizing TypeScript Properties with Proxy and Decorator - listing 4

proxy-and-decorator.ts

export function virtual( target: any, name: string)
{
    // symbol to keep the proxy handler value
    let sym = Symbol( name + "_proxy_handler");

    Object.defineProperty( target, name, {
        enumerable: true,
        
        get()
        {
            // get the proxy from the handler
            return this[sym]?.proxy;
        },

        set(v)
        {
            // check whether we already have the handler and created it if we don't
            let handler = this[sym];
            if (!handler)
                this[sym] = handler = new VirtHandler();

            // create a new proxy each time because we want the proxy to have the new value.
            handler.proxy = new Proxy( v, handler);
            
            // set the new vaule to the handler so that it will use it from now on
            handler.target = v;
        }
    });
}

class VirtHandler
{
    target: any;

    get( t: any, p: PropertyKey, r: any): any
    {
        return this.target[p];
    }
}

usage.ts

class Base
{
    @virtual first = { v: 1 };
    second = this.first;
}

class Derived extends Base
{
    first = { v: 2 };
}

let obj = new Derived();
console.log( obj.second.v);