Web-Based Customizable Staking Plans JavaScript, React, API

```javascript
// React component for a web-based customizable staking plan

import React, { useState, useEffect } from 'react';

// Mock API endpoint (replace with your actual API)
const API_ENDPOINT = 'https://example.com/api/staking';  // Replace with your real API endpoint


function StakingPlan() {
  // State variables to store staking details
  const [initialInvestment, setInitialInvestment] = useState(1000); // Default investment
  const [apy, setApy] = useState(5); // Default APY (Annual Percentage Yield)
  const [stakingDuration, setStakingDuration] = useState(365); // Default duration in days
  const [compoundingFrequency, setCompoundingFrequency] = useState(30); // Default compounding frequency in days (monthly)
  const [stakingRewards, setStakingRewards] = useState(0);
  const [isLoading, setIsLoading] = useState(false);
  const [error, setError] = useState(null);

  // useEffect hook to calculate staking rewards whenever inputs change
  useEffect(() => {
    const calculateRewards = async () => {
      setIsLoading(true); // Set loading state while fetching/calculating
      setError(null);     // Clear any previous errors

      try {
        // Option 1:  Direct Calculation in the Frontend (using Javascript)
        // Useful for simple calculations or when API interaction is not required

        const calculatedRewards = calculateStakingRewards(
          initialInvestment,
          apy,
          stakingDuration,
          compoundingFrequency
        );
        setStakingRewards(calculatedRewards);



        // Option 2:  Call an API to calculate the rewards
        //  More suitable for complex calculations or when calculations
        //  require access to backend data or specialized libraries.

        /*
        const response = await fetch(`${API_ENDPOINT}/calculate`, {
          method: 'POST',
          headers: {
            'Content-Type': 'application/json',
          },
          body: JSON.stringify({
            initialInvestment,
            apy,
            stakingDuration,
            compoundingFrequency,
          }),
        });

        if (!response.ok) {
          throw new Error(`API error: ${response.status}`);
        }

        const data = await response.json();
        setStakingRewards(data.rewards); // Assuming the API returns { rewards: ... }
        */


      } catch (err) {
        setError(err.message); // Set the error message
        setStakingRewards(0); // Reset rewards in case of error
      } finally {
        setIsLoading(false); //  Set loading state to false after calculation/API call
      }
    };

    calculateRewards(); // Call the calculation function when dependencies change
  }, [initialInvestment, apy, stakingDuration, compoundingFrequency]); // Dependencies array

  // Helper function to calculate staking rewards (using compound interest formula)
  const calculateStakingRewards = (principal, apy, durationDays, compoundingIntervalDays) => {
    const apyDecimal = apy / 100; // Convert APY to decimal
    const numberOfCompoundingPeriods = durationDays / compoundingIntervalDays;
    const interestRatePerPeriod = apyDecimal / (365 / compoundingIntervalDays);

    // Compound interest formula
    const futureValue = principal * Math.pow(1 + interestRatePerPeriod, numberOfCompoundingPeriods);
    return futureValue - principal;  // Only return the earned rewards.
  };

  return (
    <div>
      <h1>Staking Plan Calculator</h1>

      {/* Input fields for staking details */}
      <div>
        <label>Initial Investment:</label>
        <input
          type="number"
          value={initialInvestment}
          onChange={(e) => setInitialInvestment(parseFloat(e.target.value) || 0)}
        />
      </div>

      <div>
        <label>APY (%):</label>
        <input
          type="number"
          value={apy}
          onChange={(e) => setApy(parseFloat(e.target.value) || 0)}
        />
      </div>

      <div>
        <label>Staking Duration (days):</label>
        <input
          type="number"
          value={stakingDuration}
          onChange={(e) => setStakingDuration(parseInt(e.target.value) || 0)}
        />
      </div>

      <div>
        <label>Compounding Frequency (days):</label>
        <input
          type="number"
          value={compoundingFrequency}
          onChange={(e) => setCompoundingFrequency(parseInt(e.target.value) || 1)} // Prevent zero interval
        />
      </div>

      {/* Display calculated staking rewards */}
      {isLoading && <p>Loading...</p>}
      {error && <p style={{ color: 'red' }}>Error: {error}</p>}
      {!isLoading && !error && (
        <div>
          <h2>Staking Rewards: ${stakingRewards.toFixed(2)}</h2>
          <p>This is your estimated reward after {stakingDuration} days.</p>
        </div>
      )}
    </div>
  );
}

export default StakingPlan;


// Explanation:

// 1.  Import Statements:
//     - `import React, { useState, useEffect } from 'react';`: Imports necessary React hooks for state management and side effects (like calculations).

// 2. API_ENDPOINT:
//    - `const API_ENDPOINT = 'https://example.com/api/staking';`:  A placeholder for the URL of your backend API.  You'll need to replace this with your actual API endpoint.  This API would ideally handle the staking reward calculation.  The code includes an example of how to use it, but it is commented out.

// 3. StakingPlan Component:
//    - `function StakingPlan() { ... }`:  Defines a functional React component named `StakingPlan`. This component will manage the state and logic for the staking plan calculator.

// 4. State Variables (useState):
//    - `useState(1000)`: Initializes a state variable with a default value.
//    - `setInitialInvestment(parseFloat(e.target.value) || 0)`:  Updates the state when the input value changes. `parseFloat` converts the input to a number, and `|| 0` provides a default value of 0 if the input is not a valid number.
//    - `isLoading` and `error`: manage the loading state and any potential errors from API calls or calculations.

// 5. useEffect Hook:
//    - `useEffect(() => { ... }, [initialInvestment, apy, stakingDuration, compoundingFrequency]);`:  This hook runs after the component renders and whenever any of the values in the dependencies array (the second argument) change.
//       - It calls `calculateRewards()` to recalculate the rewards when any input values change.

// 6. calculateRewards function (async):
//    - `const calculateRewards = async () => { ... }`:  An asynchronous function that performs the staking reward calculation.
//       - `setIsLoading(true)`:  Sets the loading state to `true` while the calculation or API call is in progress.
//       - `setError(null)`: Clears any previous errors before starting a new calculation.
//       - try...catch: Handles potential errors during the calculation or API call.
//       - **Two calculation options are provided:**
//         - **Option 1 (Direct Calculation in Frontend):**
//           - Calculates the rewards directly in the frontend using the `calculateStakingRewards` helper function.
//         - **Option 2 (API Call):**
//           - Sends a `POST` request to your backend API (`API_ENDPOINT`) with the input values.  The API should return the calculated rewards in a JSON response. The frontend updates its state using the returned data.
//       - `finally`:  Ensures that `setIsLoading(false)` is always called, regardless of whether the calculation was successful or resulted in an error.  This is important to stop the loading indicator.

// 7. calculateStakingRewards function:
//    - `const calculateStakingRewards = (principal, apy, durationDays, compoundingIntervalDays) => { ... }`:  A helper function that calculates the staking rewards using the compound interest formula.  It takes the principal, APY, staking duration, and compounding frequency as input and returns the calculated rewards.

// 8. JSX Structure (return):
//    - The `return` statement defines the UI of the component using JSX.  It includes:
//       - A heading (`<h1>`).
//       - Input fields for initial investment, APY, staking duration, and compounding frequency.
//       - Displays loading, error or the calculated staking rewards.
//       - Conditional rendering using `isLoading`, `error`, and `stakingRewards` to display appropriate messages or data.
//       - `toFixed(2)`: Formats the staking rewards to two decimal places for currency display.

// 9.  Event Handlers:
//     - `onChange={(e) => setInitialInvestment(parseFloat(e.target.value) || 0)}`:  Handles changes to the input fields.  It calls the corresponding `set...` function to update the state with the new value.

// To use this code:

// 1.  Replace `API_ENDPOINT` with your actual backend API endpoint (if you choose to use the API approach).  If not using an API, you can remove the API-related code and just use the frontend calculation.

// 2.  Create a backend API (using Node.js, Python/Flask, etc.) that handles the `/calculate` route (or whatever you name your route) and performs the staking reward calculation.  The API should accept the input values (initialInvestment, apy, stakingDuration, compoundingFrequency) as JSON in the request body and return the calculated rewards as a JSON response.

// 3.  Install the necessary dependencies:
//    ```bash
//    npm install react react-dom
//    ```

// 4.  Render the `StakingPlan` component in your `index.js` or `App.js` file.

// This is a basic example and can be extended with more features, such as:
//   -  More complex staking options (e.g., lock-up periods, early withdrawal penalties).
//   -  Integration with a blockchain wallet to manage staking transactions.
//   -  Error handling and validation for user input.
//   -  More sophisticated UI elements and styling.
```