layout: "../layouts/BlogPost.astro" title: "Practical considerations for Input fields" slug: practical-considerations-for-input-fields description: "" added: "Jun 5 2024" updatedDate: "Aug 17 2024"
<template>
<div contenteditable="true" v-html="modelValue" @input="update"></div>
</template>
<script setup>
import { ref } from 'vue'
const modelValue = ref('')
function update(ev) {
modelValue.value = ev.target.innerHTML
}
</script>
What's the issue here? Whenever the data is updated, the DOM element refreshes with the "new" data, causing the caret to jump back to the beginning of the contenteditable div.
A quick fix is to use blur event rather than input. So if we know there's any text content change happening between the focus shift, it qualifies as a change event. However, sometimes we need the input event to detect user's typing. The key here is we only want Vue to re-render when the input stops. v-once directive can help us here to skip subsequent re-renders. Additionally, we need to mutate the editable block's content manually.
<template>
<div v-once contenteditable="true" v-html="modelValue" @input="update"></div>
</template>
<script setup>
const props = defineProps({
modelValue: {
type: String,
default: '',
},
})
const emits = defineEmits(['update:modelValue'])
function update(ev) {
if (ev.target.innerHTML !== props.modelValue) {
this.$emit('update:modelValue', ev.target.innerHTML)
}
}
</script>
By the way, elements that are made editable, and therefore interactive, by using the contenteditable attribute can be focused.
const hugeList = Array.from({ length: 30000 }, () => Math.random())
export default function App() {
const [filter, setFilter] = useState('')
return (
<div className="App">
<form>
<label>
Filter:
<input
type="text"
value={filter}
onChange={(e) => setFilter(e.target.value)}
/>
</label>
</form>
<List filter={filter} />
</div>
)
}
const List = memo(({ filter }) => (
<ul>
{hugeList
.filter((item) => item.toString().includes(filter))
.map((i) => (
<li>{i}</li>
))
}
</ul>
))
What's the issue here? When you type in the filter, it takes a long time to update. This is the problem with synchronous rendering. Let's opt into concurrent rendering. useDeferredValue is a React Hook that lets you defer updating a part of the UI, and the timeout is determined by the React scheduler, not the developer. Which means, if the React has some free cycles, it will update the deferred value, if React is too busy rendering other stuff, it not going to update the deferred value.
export default function App() {
const [filter, setFilter] = useState('')
// Used to defer updating a part of the UI.
const deferredFilter = useDeferredValue(filter)
return (
<div className="App">
<form>
<label>
Filter:
<input
type="text"
value={filter}
onChange={(e) => setFilter(e.target.value)}
/>
</label>
</form>
<List filter={deferredFilter} />
</div>
)
}
Now we're recomputing the list only when the deferred value changes, so we do it at a more opportune time for performance. To be more specific, during updates, the deferred value will “lag behind” the latest value. In particular, React will first re-render without updating the deferred value, and then try to re-render with the newly received value in the background.
A similar scenario uses useTransition hook. Both useDeferredValue and useTransition hooks are part of React's Concurrent Features and are designed to help manage expensive updates.
useTransition: Primarily for handling state updates that cause expensive re-renders.useDeferredValue: For deferring the render of less important parts of the UI.// An example written by @asidorenko_
export default function Page() {
const [tab, setTab] = useState(1)
return (
<>
<div>
<TabButton onClick={() => setTab(1)}>Tab 1</TabButton>
<TabButton onClick={() => setTab(2)}>Tab 2</TabButton>
<TabButton onClick={() => setTab(3)}>Tab 3</TabButton>
</div>
{ tab === 1 && <Tab1 /> }
{ tab === 2 && <Tab2 /> }
{ tab === 3 && <Tab3 /> }
</>
)
}
function SlowComponent() {
let startTime = performance.now()
while (performance.now() - startTime < 10)
return <li>Slow component</li>
}
function Tab2() {
const items = []
for (let i = 0; i < 100; i++) {
items.push(<SlowComponent key={i} />)
}
return <ul>{items}</ul>
}
function TabButton({ children, isActive, onClick }) {
// Used to mark updates as non-urgent.
const [isPending, startTransition] = useTransition()
return (
<button
className={cn(
isActive && "text-pink-500",
isPending && "opacity-50"
)}
onClick={() => {
startTransition(() => {
onClick()
})
}}
>
{children}
</button>
)
}
useActionState and useFormStatusReact 19 has a built-in mechanism for handling forms called "actions". Below example from Shruti Kapoor's video shows how to convert a form from React 18 to React 19.
event.preventDefault because that’s handled for us by React.action is automatically treated as a transition.useFormStatus.// React 18
function App() {
const [name, setName] = useState("");
const [isPending, setIsPending] = useState("");
const handleChange = (event) => {
setName(event.target.value);
};
const handleSubmit = (event) => {
event.preventDefault();
setIsPending(true);
setTimeout(() => {
// call API
setIsPending(false);
}, [1000]);
};
return (
<form>
<input type="text" name="name" onChange={handleChange} />
{ isPending ? <p>{"Loading"}</p> : <p> Hello in React 18 {name}</p> }
<button onClick={handleSubmit} disabled={isPending}>
Update
</button>
</form>
);
}
// React 19
function RenderName({ name }) {
// https://react.dev/reference/react-dom/hooks/useFormStatus
// The `useFormStatus` hook only returns status information for a parent <form>
const { pending } = useFormStatus();
return <div>{pending ? "Loading" : `Hello in React 19 ${name}` }</div>;
}
function SubmitButton() {
const { pending } = useFormStatus();
return (
<button type="submit" disabled={pending}>
Update
</button>
);
}
function App() {
// https://react.dev/reference/react/useActionState
// You pass `useActionState` an existing form action function as well as an initial state,
// and it returns a new action that you use in your form, along with the latest form state.
// The latest form state is also passed to the function that you provided.
const [state, formAction] = useActionState(submitFormAction, { name: "" });
return (
<form action={formAction}>
<input type="text" name="inputName" />
<RenderName name={state?.name} />
<SubmitButton />
</form>
);
}
// actions.js
'use server';
export const submitFormAction = async (previousState, formData) => {
const name = formData.get("name");
await new Promise((res) => setTimeout(res, 1000));
return { ...previousState, name: name };
};
There is another example from React Conf 2024 displaying a message box, which is progressively enhanced with React 19 features. The main functionality of the form works without JavaScript.
// https://www.youtube.com/watch?v=X9cw4VczYVg
export default function MessageInput({ userId }) {
const [state, submitMessageAction] = useActionState(submitMessage, {
success: false,
});
useEffect(() => {
if (state.error) {
toast.error(state.error);
}
}, [state.error, state.timestamp]);
return (
<>
<form action={submitMessageAction} className="flex flex-col gap-2 p-6">
<input
autoComplete="off"
required
minLength={1}
name="content"
className="italic outline-none"
placeholder="Type a message..."
/>
<input type="hidden" name="userId" value={userId} />
{/* get pending status using `useFormStatus()` inside the button component */}
<SubmitButton>Send</SubmitButton>
</form>
</>
);
}
export async function submitMessage(_prevState, formData) {
// z.object({
// content: z.string().min(1, {
// message: 'Content must be at least 1 characters long',
// }),
// createdById: z.string().uuid({
// message: 'Invalid user ID',
// }),
// });
const result = messageSchema.safeParse({
content: formData.get('content'),
createdById: formData.get('userId'),
});
if (!result.success) {
return {
error: 'Invalid message!',
success: false,
timestamp: new Date(),
};
}
await prisma.message.create({
data: result.data,
});
revalidatePath('/');
return {
success: true,
};
}
The :user-valid and :user-invalid pseudo-class selectors are similar to the existing :valid and :invalid pseudo-classes. Both match a form control based on whether its current value satisfies its validation constraints. However, the advantage of the new :user-valid and :user-invalid pseudo-classes is that they match a form control only after a user has significantly interacted with the input.
A form control that is required and empty will match :invalid even if a user has not started interacting with the page. However, that same form control won't match :user-invalid until the user has changed the input and left it in an invalid state.
:user-validand:user-invalidare available in all three browser engines (Chrome 119+)
input:user-valid {
border: 2px solid green;
}
input:user-valid + span::before {
content: "✓";
color: green;
}
input:user-invalid {
border: 2px solid red;
}
input:user-invalid + span::before {
content: "✖";
color: red;
}