Class FormData

tests/unit/utils.test.js:46–52

    it('should detect custom FormData instances by toStringTag signature and append method presence', () => {
      class FormData {
        append() {}

        get [Symbol.toStringTag]() {
          return 'FormData';
        }
      }
      assert.equal(utils.isFormData(new FormData()), true);
    });
  });