ES6 proxy work-around for "TypeError: Cannot create proxy with a non-object as target"?

My last question here: How to store data of a functional chain of Monoidal List?

had many great responses and one of them suggested to implement some sort of type structure in JavaScript:

 const TYPE = Symbol();
  const typeOf = t => x => x == null
    ? x
    : Object.assign(x, {
      [TYPE]: t
    });

  const isType = t => x => x == null
    ? false
    : x[TYPE] === t;

  const Foo = x => typeOf(Foo)(x);

  console.log(
    isType(Foo)(1) // false
    , isType(Foo)([]) // false
    , isType(Foo)({}) // false
    , isType(Foo)(x => x) // false
    , isType(Foo)(true) // false
    , isType(Foo)(undefined) // false
    , isType(Foo)(null) // false
  );
 
  console.log(
    isType(Foo)(Foo(1)) // true
    , isType(Foo)(Foo([])) // true
    , isType(Foo)(Foo({})) // true
    , isType(Foo)(Foo(x => x)) // true
    , isType(Foo)(Foo(true)) // true
    , isType(Foo)(Foo(undefined)) // false
    , isType(Foo)(Foo(null)) // false
  );

  console.log(Foo(1) + Foo(2)); //3
 

While I thought this is a great idea, another member suggests this is inconsistent since Object.assign is a mutable operation and it should not be allowed in Functional Programming context.

In response, there is another idea to use Proxy instead, so I have tried to implement the similar system by myself.

The result is unfortunately very poor since Proxy seems only to accept Object.

Works as the expample

var target = {};
var p = new Proxy(target, {});

p.a = 37; // operation forwarded to the target

console.log(target.a); // 37. The operation has been properly forwarded
 

"Uncaught TypeError: Cannot create proxy with a non-object as target or handler"

var target = 5;
var p = new Proxy(target, {});

p.a = 37; // operation forwarded to the target

console.log(target.a); // 37. The operation has been properly forwarded
 

I also considered to take advantage of Object.create, but does not work in similar manner of Proxy.

Basically, I recognize this is a challenge to implement Inheritance (object-oriented programming) in functional programming with the dynamic typing　and reflection.

Therefore, I really want to make this implementation work in ES6 Proxy context.

Any great ideas? Thanks.