tiny getter/setter helper for observables, polyfilling, deprecation, interfacing, etc

odp.js

function odp(obj, get, set, isHidden){
   Object.defineProperty(obj, /^\w+/.exec(get), {get, set, enumerable: !isHidden});
  return odp.bind(this, obj);
}

// example usage in a class
class Ohm {
 constructor(V, I){
   odp(this, _=>Ohm)
    ( v=>V,   _=>V=_   )
    ( i=>I,   _=>I=_   )
    ( w=>V*I, _=>I=_/V )
    ( r=>V/I, _=>I=V/_ );
 }
}
var x = new Ohm(5, 2);          // == {"v":5,"i":2,"w":10,"r":2.5}
x.r=10;
console.log(JSON.stringify(x)); // == {"v":5,"i":0.5,"w":2.5,"r":10}



// example usage in a factory
function Ohm (V, I, _){
   odp(_={}, _=>Ohm)
    ( v=>V,   _=>V=_   )
    ( i=>I,   _=>I=_   )
    ( w=>V*I, _=>I=_/V )
    ( r=>V/I, _=>I=V/_ );
  return _;
}
var y = Ohm(5, 2);              // == {"v":5,"i":2,"w":10,"r":2.5}
y.r=10;
console.log(JSON.stringify(y)); // == {"v":5,"i":0.5,"w":2.5,"r":10}



// example usage  w/ state in lexical scope
let V=5, I=2, z={}; 
 odp( z,      _=>odp   )
    ( v=>V,   _=>V=_   )
    ( i=>I,   _=>I=_   )
    ( w=>V*I, _=>I=_/V )
    ( r=>V/I, _=>I=V/_ );

console.log(JSON.stringify(z)); // == {"v":5,"i":2,"w":10,"r":2.5}
z.r=10;
console.log(JSON.stringify(z)); // == {"v":5,"i":0.5,"w":2.5,"r":10}



/* compare to inline getters and setters:

function Ohm(o){
 return Object.assign({
   get v(){return o.v;},
   get i(){return o.i;},
   get w(){return o.v * o.i},
   get r(){return o.v / o.i},

   set v(val){return o.v=val;},
   set i(val){return o.i=val;},
   set r(val){ o.i = o.v / val;},
   set w(val){ o.i = val / o.v;},
 }, o);
}




*/