fix: make it compatible with node's --disable-proto=throw (#78)

* fix: make it compatible with node's --disable-proto

Many people use the option `--disable-proto` in NodeJS to minimise the probability of prototype pollution attacks. Because of that, `__proto__` might not be available.

* refactor: move conditional outside hotpath

* refactor: avoid _ prefix for getPrototypeOf

* fix: add missing parenthesis

Signed-off-by: Andres Correa Casablanca <castarco@coderspirit.xyz>

---------

Signed-off-by: Andres Correa Casablanca <castarco@coderspirit.xyz>

src/index.ts

@@ -22,7 +22,8 @@ import type { InternalCopier, State } from './copier';
 export type { State } from './copier';
 
 const { isArray } = Array;
-const { assign, getPrototypeOf } = Object;
+const { assign } = Object;
+const getPrototypeOf = Object.getPrototypeOf || ((obj) => obj.__proto__)
 
 export interface CreateCopierOptions {
   array?: InternalCopier<any[]>;
@@ -116,7 +117,7 @@ export function createCopier(options: CreateCopierOptions) {
       return state.cache.get(value);
     }
 
-    state.prototype = value.__proto__ || getPrototypeOf(value);
+    state.prototype = getPrototypeOf(value);
     state.Constructor = state.prototype && state.prototype.constructor;
 
     // plain objects