React Hook Form Dynamic Require - validation

Question

Good Day All,
Im using react hook form and I want set required dynamically on one text-input. I have a useState that tracks the delivery method and radio buttons that update that state. And then the text-input required should be based dynamically on that state. So if the delivery method is "Delivery" we require your address if its "Pickup" we dont require your address. I hope that makes sense.
In the code below the show/hide functionality works as expected however the dynamic require does not.
const [ delivery, setDelivery ] = useState(false);
<InfoBlock>
<strong>Delivery Method</strong>
<RadioGroup>
<RadioBlock>
<input type="radio" id="pickup" name="pickup" {...register("deliveryMethod", {required: true})}
value="pickup" onClick={() => setDelivery(false)} />
<h5>Pickup</h5>
</RadioBlock>
<RadioBlock>
<input type="radio" id="deliver" name="delivery" {...register("deliveryMethod", {required: true})}
value="delivery" onClick={() => setDelivery(true)} />
<h5>Delivery</h5>
</RadioBlock>
</RadioGroup>
</InfoBlock>
<ErrorMsg>
{errors.deliveryMethod && errors.deliveryMethod.type === 'required' && "Please select delivery method"}
</ErrorMsg>
{delivery ?
<div>
<InfoBlock>
<strong>Address</strong>
**<input type="text" id="address" name="address"
{...register("address", {required: delivery })} />**
</InfoBlock>
<ErrorMsg>
{errors.address && errors.address.type === 'required' && "Address is required"}
</ErrorMsg>
</div> : null}

Answer 1

You don't need useState here, as you can use RHF for handling the state of your radio input value - you can just use watch, provided by useForm, to watch for changes of that field
As you conditionally render the 'address' input only for a certain delivery method, you can also just set required to true for the rules of that field
There is one important thing: since v7 there is no automatically removal of fields which will unmount (in your case, due to conditional rendering). So for now, you have to unregister the field manually. This is why in the CodeSandbox there is the unregister call, when clicking the 'pickup' radio option.
However, there is currently a discussion ongoing, as this new behaviour brings disadvantages in some cases (such as conditional rendering of fields). So maybe it will be possible again in the future to unregister fields automatically on unmount.