unified-formik-field-extractInputProps3.js

else if (props.type === 'checkbox') {
  props.value = option.value;
  props.checked = formik.values[props.name].includes(option.value);
  props.onChange = e => {
    const val = formik.values[props.name];
    e.target.checked
      ? val.push(e.target.value)
      : val.slice(val.indexOf(e.target.value));
    formik.setFieldValue(val);
  }
}