fix: fixed output when passed into JSON.stringify (#19)

src/Filterion.spec.ts

@@ -509,6 +509,28 @@ describe('filterion.getValues', () => {
   });
 });
 
+describe('filterion.toJSON', () => {
+  it('stringified representation matches the payload repesentation', () => {
+    const filterion = new Filterion<MyTestFilter>()
+      .add('name', 'Max');
+    const payload = filterion.getPayload();
+
+    const json = JSON.stringify(filterion);
+    const payloadJson = JSON.stringify(payload);
+
+    expect(json).toStrictEqual(payloadJson);
+  });
+  it('toJSON result matches the payload', () => {
+    const filterion = new Filterion<MyTestFilter>()
+      .add('name', 'Max');
+    const payload = filterion.getPayload();
+
+    const toJsonResult = filterion.toJSON();
+
+    expect(toJsonResult).toStrictEqual(payload);
+  })
+});
+
 type MyTestFilter = {
   name: string;
   age: number;

src/Filterion.ts

@@ -201,12 +201,22 @@ export class Filterion<S extends {} = {}> {
     return new Filterion<S>(this.config).attach(payloadClone);
   }
 
+  /*
+   * Attach existing payload
+   */
   public attach(payload: IFilterionPayload<S>): Filterion<S> {
     const result = new Filterion<S>(this.config);
     result.payload = payload;
     return result;
   }
 
+  /*
+   * Get JSON representation of the instance
+   */
+  public toJSON(): IFilterionPayload<S> {
+    return this.payload;
+  }
+
   /**
    * Initialize payload"s values collection if it doesn"t exist yet
    */