add formal support for primitive wrappers

CHANGELOG.md

@@ -13,6 +13,7 @@
 **Enhancements**
 
 - Can now create a custom copier, allowing maximum performance for specific use-cases
+- Correctly handle primitive wrappers, e.g. `new String('foo')`
 
 ## 2.1.7
 

DEV_ONLY/App.ts

@@ -27,6 +27,7 @@ const object: PlainObject = {
   arrayBuffer: new ArrayBuffer(8),
   blob: new Blob(['<a id="a">hey!</a>'], { type: 'text/html' }),
   boolean: true,
+  booleanConstructor: new Boolean(true),
   customPrototype: Object.create({
     method() {
       return 'foo';
@@ -56,6 +57,7 @@ const object: PlainObject = {
   nan: NaN,
   nil: null,
   number: 123,
+  numberConstructor: new Number('123'),
   object: { foo: { bar: 'baz' } },
   promise: Promise.resolve('foo'),
   react: React.createElement('main', {
@@ -83,6 +85,7 @@ const object: PlainObject = {
   regexp: /foo/gi,
   set: new Set().add('foo').add({ bar: 'baz' }),
   string: 'foo',
+  stringConstructor: new String('foo'),
   symbol: Symbol('foo'),
   typedArray: new Uint8Array([12, 15]),
   undef: undefined,

__tests__/copier.ts

@@ -212,6 +212,30 @@ describe('copyMapStrict', () => {
   });
 });
 
+describe('copyPrimitiveWrapper', () => {
+  it('will create a copy of the value of the primitive in a new wrapper', () => {
+    const boolean = new Boolean(true);
+    const number = new Number('123');
+    const string = new String('foo');
+
+    [boolean, number, string].forEach((primitiveWrapper) => {
+      const mockCopier = jest.fn().mockImplementation((arg) => arg);
+      const cache = createCache();
+      const prototype = Object.getPrototypeOf(primitiveWrapper);
+
+      const result = copier.copyPrimitiveWrapper(primitiveWrapper, {
+        Constructor: prototype.constructor,
+        cache,
+        copier: mockCopier,
+        prototype,
+      });
+
+      expect(result).not.toBe(primitiveWrapper);
+      expect(result).toEqual(primitiveWrapper);
+    });
+  });
+});
+
 describe('copySetStrict', () => {
   it('will copy both values and explicit properties', () => {
     const object: any = new Set(['foo', 'bar']);

src/copier.ts

@@ -250,6 +250,17 @@ export function copyObjectStrict<Value extends Record<string, any>>(
   return copyOwnPropertiesStrict(object, clone, state);
 }
 
+/**
+ * Create a new primitive wrapper from the value of the original.
+ */
+export function copyPrimitiveWrapper<
+  // Specifically use the object constructor types
+  // eslint-disable-next-line @typescript-eslint/ban-types
+  Value extends Boolean | Number | String
+>(primitiveObject: Value, state: State): Value {
+  return new state.Constructor(primitiveObject.valueOf());
+}
+
 /**
  * Create a new RegExp based on the value and flags of the original.
  */

src/index.ts

@@ -9,6 +9,7 @@ import {
   copyMapStrict,
   copyObjectLoose,
   copyObjectStrict,
+  copyPrimitiveWrapper,
   copyRegExp,
   copySelf,
   copySetLoose,
@@ -66,9 +67,11 @@ function getTagSpecificCopiers(
   options: Required<CreateCopierOptions>
 ): Record<string, InternalCopier<any>> {
   return {
+    Arguments: options.object,
     Array: options.array,
     ArrayBuffer: options.arrayBuffer,
     Blob: options.blob,
+    Boolean: copyPrimitiveWrapper,
     DataView: options.dataView,
     Date: options.date,
     Error: options.error,
@@ -78,10 +81,12 @@ function getTagSpecificCopiers(
     Int16Array: options.arrayBuffer,
     Int32Array: options.arrayBuffer,
     Map: options.map,
+    Number: copyPrimitiveWrapper,
     Object: options.object,
     Promise: copySelf,
     RegExp: options.regExp,
     Set: options.set,
+    String: copyPrimitiveWrapper,
     WeakMap: copySelf,
     WeakSet: copySelf,
     Uint8Array: options.arrayBuffer,