Building a library like react-stripe-js requires abstracting complex native SDK interactions into simple, reusable React components and hooks, while ensuring a seamless user experience. This involves creating a Provider to initialize the library, hooks (useElements, useClient) to access the initialized instance, and components (CardElement, PaymentRequestButtonElement) to securely render payment fields via iframes. Below is a conceptual outline and an example of how you might structure the core components of such a library.

Library Architecture

The library revolves around a central PaymentGatewayProvider that initializes the underlying non-React SDK and a custom React context to expose that instance to all child components and hooks. This mimics the architecture of most professional payment gateway SDKs.

1. Core Hooks and Context (src/context.js)

This manages the React context for sharing the initialized gateway instance (clientInstance) and element management utilities.

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

const PaymentGatewayContext = createContext(null);

export const PaymentGatewayProvider = ({ children, clientKey }) => {
  const [clientInstance, setClientInstance] = useState(null);
  const [elements, setElements] = useState(null);

  useEffect(() => {
    // In a real library, you would load an external JS SDK here
    // e.g., const gatewaySDK = loadExternalSDK(clientKey);
    // setClientInstance(gatewaySDK);
    // setElements(gatewaySDK.elements());

    // Mock implementation for demonstration:
    const mockGateway = {
        elements: () => ({
            create: (type, options) => ({
                mount: (domElement) => console.log(`Mounting ${type} to ${domElement.id}`),
                on: (event, handler) => console.log(`Listening for ${event}`),
                // Mock methods for confirm calls
                confirmCardPayment: async (clientSecret, paymentMethod) => ({
                    paymentIntent: { status: 'succeeded' }
                })
            })
        }),
        confirmCardPayment: async (clientSecret, options) => ({
            paymentIntent: { status: 'succeeded' }
        })
    };
    setClientInstance(mockGateway);
    setElements(mockGateway.elements());
  }, [clientKey]);

  return (
    <PaymentGatewayContext.Provider value={{ clientInstance, elements }}>
      {children}
    </PaymentGatewayContext.Provider>
  );
};

export const useClient = () => useContext(PaymentGatewayContext).clientInstance;
export const useElements = () => useContext(PaymentGatewayContext).elements;

2. Generic Element Component (src/Element.js)

This reusable component renders a generic payment field securely within an iframe and manages its lifecycle.

import React, { useRef, useEffect, useState } from 'react';
import { useElements } from './context';

export const Element = ({ id, type, options, onChange }) => {
  const elements = useElements();
  const elementRef = useRef(null);
  const [elementInstance, setElementInstance] = useState(null);

  useEffect(() => {
    if (elements && elementRef.current) {
      const element = elements.create(type, options);
      element.mount(elementRef.current);
      if (onChange) {
        element.on('change', onChange);
      }
      setElementInstance(element);
    }
  }, [elements, options, type, onChange]);

  // Clean up element on unmount
  useEffect(() => {
    return () => {
        if (elementInstance) {
            elementInstance.destroy();
        }
    };
  }, [elementInstance]);

  return <div id={id} ref={elementRef} />;
};

3. Specific Payment Method Components (src/CardElement.js)

You create specific components for different payment methods as simple wrappers around the generic Element.

import React from 'react';
import { Element } from './Element';

export const CardElement = (props) => (
  <Element id="card-element" type="card" {...props} />
);

Usage Example (src/App.js or Merchant App)

The merchant using your library would integrate it like this:

import React, { useState } from 'react';
import { PaymentGatewayProvider, CardElement, useClient, useElements } from './context'; // from 'your-gateway-library'

const CheckoutForm = () => {
  const client = useClient();
  const elements = useElements();
  const [loading, setLoading] = useState(false);
  const [status, setStatus] = useState('');

  const handleSubmit = async (event) => {
    event.preventDefault();
    setLoading(true);

    if (!client || !elements) {
      return;
    }
    
    // Get a reference to a mounted element
    const cardElement = elements.create('card'); // In a real app, you'd use the instance from the ref/state

    // Use the client library to confirm the payment
    const result = await client.confirmCardPayment('MOCK_CLIENT_SECRET_FROM_BACKEND', {
      payment_method: {
        card: cardElement,
        billing_details: { name: 'John Doe' },
      },
    });

    if (result.error) {
      setStatus(`Error: ${result.error.message}`);
    } else {
      setStatus(`Payment status: ${result.paymentIntent.status}`);
    }
    setLoading(false);
  };

  return (
    <form onSubmit={handleSubmit} style={{ padding: '20px', border: '1px solid #ccc' }}>
      <label>
        Card Details
        {/* The CardElement securely renders the iframe */}
        <CardElement onChange={(event) => console.log('Element changed:', event.complete)} />
      </label>
      <button type="submit" disabled={loading} style={{ marginTop: '15px' }}>
        {loading ? 'Processing...' : 'Pay'}
      </button>
      <p>{status}</p>
    </form>
  );
};


const MerchantApp = () => {
  return (
    // Initialize the provider with the merchant's key
    <PaymentGatewayProvider clientKey="pk_test_MERCHANT_KEY">
      <h1>My Store Checkout</h1>
      <CheckoutForm />
    </PaymentGatewayProvider>
  );
};

// export default MerchantApp;