`onButtonDisabled`

[DmitriiMelnikOnix]

onButtonDisabled = () => {
    const { formData } = this.state;
    if (formData.checkedMail && !formData.isMailError && formData.touchedMail) {
      return false;
    }
    return true;
  };

if зайвий, можна спростити

onButtonDisabled = () => {
    const { formData } = this.state;
    return !(formData.checkedMail && !formData.isMailError && formData.touchedMail);
};

[dimakrugly]

Done