State এর সঙ্গে Input-র upor প্রতিক্রিয়া

কীভাবে ঘোষণামূলক UI অপরিহার্য UI-র সাথে তুলনা করে

আপনি যখন UI ইন্টারঅ্যাকশন ডিজাইন করেন, আপনি সম্ভবত ব্যবহারকারীর ক্রিয়াকলাপের প্রতিক্রিয়ায় UI কীভাবে পরিবর্তিত হয় সে সম্পর্কে চিন্তা করেন। এমন একটি ফর্ম বিবেচনা করুন যা ব্যবহারকারীকে একটি উত্তর জমা দিতে দেয়:

• আপনি যখন ফর্মে কিছু টাইপ করেন, তখন “জমা দিন” বোতামটি সক্রিয় হয়ে যায়।
• আপনি যখন “জমা দিন” টিপুন, ফর্ম এবং বোতাম উভয়ই নিষ্ক্রিয় হয়ে যায় এবং একটি স্পিনার উপস্থিত হয়।
• নেটওয়ার্ক অনুরোধ সফল হলে, ফর্মটি লুকানো হবে এবং “ধন্যবাদ” বার্তাটি প্রদর্শিত হবে।
• নেটওয়ার্ক অনুরোধ ব্যর্থ হলে, একটি ত্রুটি বার্তা প্রদর্শিত হবে, এবং ফর্ম আবার সক্রিয় হয়ে যাবে ।

In imperative programming, the above corresponds directly to how you implement interaction. You have to write the exact instructions to manipulate the UI depending on what just happened. Here’s another way to think about this: imagine riding next to someone in a car and telling them turn by turn where to go.

They don’t know where you want to go, they just follow your commands. (And if you get the directions wrong, you end up in the wrong place!) It’s called imperative because you have to “command” each element, from the spinner to the button, telling the computer how to update the UI.

In this example of imperative UI programming, the form is built without React. It only uses the browser DOM:

Manipulating the UI imperatively works well enough for isolated examples, but it gets exponentially more difficult to manage in more complex systems. Imagine updating a page full of different forms like this one. Adding a new UI element or a new interaction would require carefully checking all existing code to make sure you haven’t introduced a bug (for example, forgetting to show or hide something).

React বানানোই হয়েছিল এই সমস্যাটি সমাধান করার জন্য।

In React, you don’t directly manipulate the UI—meaning you don’t enable, disable, show, or hide components directly. Instead, you declare what you want to show, and React figures out how to update the UI. Think of getting into a taxi and telling the driver where you want to go instead of telling them exactly where to turn. It’s the driver’s job to get you there, and they might even know some shortcuts you haven’t considered!

ঘোষণামূলকভাবে UI সম্পর্কে চিন্তা করা

আপনি উপরে দেখেছেন কিভাবে একটি ফর্ম অপরিহার্যভাবে বাস্তবায়ন করতে হয়। React-এ কীভাবে চিন্তা করতে হয় তা আরও ভালোভাবে বোঝার জন্য, আপনি React-এ এই UI পুনরায় প্রয়োগ করবেন:

1. কম্পোনেন্ট এর বিভিন্ন ভিজুয়্যাল states চিহ্নিত করা
2. State-র পরিবর্তনের কারণ কী তা নির্ধারণ করুন
3. useState ব্যবহার করে মেমরিতে রাষ্ট্রের প্রতিনিধিত্ব করুন
4. কোনো অপ্রয়োজনীয় state ভেরিয়েবল কে সরিয়ে দিন
5. state সেট করতে ইভেন্ট হ্যান্ডলারদের সাথে সংযোগ করুন

Step 1: Identify your component’s different visual states

In computer science, you may hear about a “state machine” being in one of several “states”. If you work with a designer, you may have seen mockups for different “visual states”. React stands at the intersection of design and computer science, so both of these ideas are sources of inspiration.

First, you need to visualize all the different “states” of the UI the user might see:

• Empty: Form has a disabled “Submit” button.
• Typing: Form has an enabled “Submit” button.
• Submitting: Form is completely disabled. Spinner is shown.
• Success: “Thank you” message is shown instead of a form.
• Error: Same as Typing state, but with an extra error message.

Just like a designer, you’ll want to “mock up” or create “mocks” for the different states before you add logic. For example, here is a mock for just the visual part of the form. This mock is controlled by a prop called status with a default value of 'empty':

You could call that prop anything you like, the naming is not important. Try editing status = 'empty' to status = 'success' to see the success message appear. Mocking lets you quickly iterate on the UI before you wire up any logic. Here is a more fleshed out prototype of the same component, still “controlled” by the status prop:

import Form from './Form.js';

let statuses = [
  'empty',
  'typing',
  'submitting',
  'success',
  'error',
];

export default function App() {
  return (
    <>
      {statuses.map(status => (
        <section key={status}>
          <h4>Form ({status}):</h4>
          <Form status={status} />
        </section>
      ))}
    </>
  );
}

Step 2: Determine what triggers those state changes

You can trigger state updates in response to two kinds of inputs:

• Human inputs, like clicking a button, typing in a field, navigating a link.
• Computer inputs, like a network response arriving, a timeout completing, an image loading.

In both cases, you must set state variables to update the UI. For the form you’re developing, you will need to change state in response to a few different inputs:

• Changing the text input (human) should switch it from the Empty state to the Typing state or back, depending on whether the text box is empty or not.
• Clicking the Submit button (human) should switch it to the Submitting state.
• Successful network response (computer) should switch it to the Success state.
• Failed network response (computer) should switch it to the Error state with the matching error message.

To help visualize this flow, try drawing each state on paper as a labeled circle, and each change between two states as an arrow. You can sketch out many flows this way and sort out bugs long before implementation.

Step 3: Represent the state in memory with useState

Next you’ll need to represent the visual states of your component in memory with useState. Simplicity is key: each piece of state is a “moving piece”, and you want as few “moving pieces” as possible. More complexity leads to more bugs!

Start with the state that absolutely must be there. For example, you’ll need to store the answer for the input, and the error (if it exists) to store the last error:

const [answer, setAnswer] = useState('');
const [error, setError] = useState(null);

Then, you’ll need a state variable representing which one of the visual states that you want to display. There’s usually more than a single way to represent that in memory, so you’ll need to experiment with it.

If you struggle to think of the best way immediately, start by adding enough state that you’re definitely sure that all the possible visual states are covered:

const [isEmpty, setIsEmpty] = useState(true);
const [isTyping, setIsTyping] = useState(false);
const [isSubmitting, setIsSubmitting] = useState(false);
const [isSuccess, setIsSuccess] = useState(false);
const [isError, setIsError] = useState(false);

Your first idea likely won’t be the best, but that’s ok—refactoring state is a part of the process!

Step 4: Remove any non-essential state variables

You want to avoid duplication in the state content so you’re only tracking what is essential. Spending a little time on refactoring your state structure will make your components easier to understand, reduce duplication, and avoid unintended meanings. Your goal is to prevent the cases where the state in memory doesn’t represent any valid UI that you’d want a user to see. (For example, you never want to show an error message and disable the input at the same time, or the user won’t be able to correct the error!)

Here are some questions you can ask about your state variables:

• Does this state cause a paradox? For example, isTyping and isSubmitting can’t both be true. A paradox usually means that the state is not constrained enough. There are four possible combinations of two booleans, but only three correspond to valid states. To remove the “impossible” state, you can combine these into a status that must be one of three values: 'typing', 'submitting', or 'success'.
• Is the same information available in another state variable already? Another paradox: isEmpty and isTyping can’t be true at the same time. By making them separate state variables, you risk them going out of sync and causing bugs. Fortunately, you can remove isEmpty and instead check answer.length === 0.
• Can you get the same information from the inverse of another state variable? isError is not needed because you can check error !== null instead.

After this clean-up, you’re left with 3 (down from 7!) essential state variables:

const [answer, setAnswer] = useState('');
const [error, setError] = useState(null);
const [status, setStatus] = useState('typing'); // 'typing', 'submitting', or 'success'

You know they are essential, because you can’t remove any of them without breaking the functionality.

Step 5: Connect the event handlers to set state

Lastly, create event handlers that update the state. Below is the final form, with all event handlers wired up:

Although this code is longer than the original imperative example, it is much less fragile. Expressing all interactions as state changes lets you later introduce new visual states without breaking existing ones. It also lets you change what should be displayed in each state without changing the logic of the interaction itself.