Authentication with Facebook API is necessary to access certain features like user data, posts, etc. Facebook provides an OAuth 2.0 authentication protocol to authenticate users and obtain an access token. In order to use this protocol with React, we need to follow a few steps. Let's dive in.

Step 1: Create a Facebook App and Get App ID and App Secret

To use Facebook authentication with your React app, you first need to create a Facebook app on the Facebook Developer Portal. After creating the app, you can find your App ID and App Secret in the app's dashboard.

Step 2: Install the Facebook SDK and React Facebook Login package

To use the Facebook API with React, we need to install the Facebook SDK and the `react-facebook-login` package using the npm package manager. Run the following command in your terminal:

```
npm install facebook-sdk react-facebook-login
```

Step 3: Initialize the Facebook SDK

In order to use the Facebook SDK, we need to initialize it with our App ID. We can do this by adding the following code to our React component:

```typescript
import React, { useEffect } from 'react';
import FacebookLogin from 'react-facebook-login';

const App = () => {
  useEffect(() => {
    window.fbAsyncInit = function() {
      window.FB.init({
        appId            : 'YOUR_APP_ID',
        autoLogAppEvents : true,
        xfbml            : true,
        version          : 'v10.0'
      });
    };
 
    (function(d, s, id) {
      let js, fjs = d.getElementsByTagName(s)[0];
      if (d.getElementById(id)) return;
      js = d.createElement(s); js.id = id;
      js.src = "https://connect.facebook.net/en_US/sdk.js";
      fjs.parentNode.insertBefore(js, fjs);
    }(document, 'script', 'facebook-jssdk'));
  }, []);

  return (
    <div>
      {/* your component code here */}
    </div>
  );
};

export default App;
```

I﻿n the above if you are using Typescript and the compiler complains that `window.FB` does not exist, simply change this line to `(window as any).FB`.

In the `window.fbAsyncInit` function, we initialize the Facebook SDK with our App ID and set the version to use. In the `useEffect` hook, we load the Facebook SDK asynchronously and set the SDK to auto-log app events.

Step 4: Add Facebook Login Button

To allow users to authenticate with Facebook, we need to add a Facebook Login button to our React component. We can use the `react-facebook-login` package to add this button. Add the following code to your component:

```typescript
import React, { useEffect } from 'react';
import FacebookLogin from 'react-facebook-login';

const App = () => {
  useEffect(() => {
    // Initialize Facebook SDK here from above
  }, []);

  const responseFacebook = (response) => {
    console.log(response);
  };

  return (
    <div>
      <FacebookLogin
        appId="YOUR_APP_ID"
        autoLoad={false}
        fields="name,email,picture"
        callback={responseFacebook}
        scope="ads_read,ads_management"
      />
    </div>
  );
};

export default App;
```

In the `FacebookLogin` component, we set the `appId` to our App ID and specify the `fields` we want to retrieve from the user's Facebook profile. We also provide a `callback` function.

T﻿he additional `scope` requests access to the Facebook user's Ads data which is available if they have been running ads on the Facebook platform.

T﻿he callback function will receive the user's authentication token which can be added to subsequent requests to other Facebook API endpoints to authenticate and return data in the context of that user.

This post will be discussing how to authenticate with the Facebook API using OAuth2, React and requesting the required scopes to access the Facebook Ads/Marketing API.

How to Authenticate with Facebook using OAuth2 and React

Quite often as a frontend developer, you will want to use a string returned from an API as a header or a label in one way or another. Perhaps as a tab title or in a card for a dashboard.\

Unfortunately, the API may not be aware of this, nor capable of returning a string formatted in a nice way to allow the label to be human-readable.

Luckily, we can use replace and a regex to format the string in a cleaner way for us to display:

```typescript
const stringFromApi = 'UserAccountDetails';
const formattedString = stringFromApi.replace(/([a-z])([A-Z])/g, '$1 $2').trim();
console.log(formattedString); // 'User Account Details'
```

T﻿his is a pretty simple regular expression that looks globally in the string for where the lower and uppercase characters are in the string and the replace function second argument puts a space between them.

Quite often as a frontend developer, you will want to use a string returned from an API as a header or a label in one way or another. Perhaps as a tab title or in a card for a dashboard.
Unfortunately, the API may not be aware of this, nor capable of returning a string formatted in a nice way to allow the label to be human-readable.


Using Regex to Add Spaces Before Capital Letters in a String

## W﻿hat is a Recursive Function?

T﻿he short answer to this is: A recursive function is a function that somewhere in its own logic makes a request to call itself again because the same set of logic needs to be executed again.

Recursion is a fundamental concept in computer science and is used in a wide variety of algorithms and data structures.

T﻿he key to understanding how to use a recursive function is to understand how to handle the changing of function arguments to ensure there is an exit condition so the function does not call itself forever (like a while loop that never breaks the 'true' condition).

W﻿hen used properly, recursive functions are a powerful tool for solving complex coding requirements.

A﻿ simple, contrived, example of a recursive function is a countdown function:

```typescript
// Function definition
function countdown(n) {
  if (n === 0) {
    console.log("Done!");
  } else {
    console.log(n);
    countdown(n - 1);
  }
}

// Initiate the function
countdown(5);
```

T﻿he above is a simple function that counts down from a given starting value (greater than zero) and logs "Done!" when the value gets to zero. You can see that the function logs the value of the number, then requests the same function to run again, but takes one from the given value until the value is zero where it does not request to call itself again.

N﻿ow, obviously this is a contrived example and could also be achieved with a simple for loop:

```typescript
for(let i = 5; i >= 0; i--) {
  if(i !== 0) {
    console.log(i);
  } else {
    console.log('Done!');
  }
}
```

S﻿o, what is a more 'real world' use case for recursive functions?

W﻿hilst there are many, one that has presented itself frequently during my career is traversing folder directories:

```typescript
const fs = require('fs');

function listFiles(dir) {
  const files = fs.readdirSync(dir);
  for (const file of files) {
    const filePath = `${dir}/${file}`;
    const stats = fs.statSync(filePath);
    if (stats.isDirectory()) {
      listFiles(filePath);
    } else {
      console.log(filePath);
    }
  }
}

listFiles('/path/to/directory');
```

T﻿his recursive function accepts a directory path as its starting argument and then reads the directory using the NodeJs 'fs' module.

I﻿f the directory is a folder (isDirectory()) then the function is requested again with the updated path to the child folder directory.

I﻿n a real application, instead of logging the file path of the full file contained within the directory, the application would perhaps read the file and process the data (maybe a CSV of rows to insert into a database).

T﻿hese examples are a very simple introduction to the concept of recursion. There are many more complicated uses for recursion in the data science fields where complex algorithms need to be applied to data sets or in applications where algorithms are required to optimise performance to fine degrees.

You'll often hear or read that a recursive function was used to solve a programming problem that arose during the development of a piece of software. So, what is a recursive function, how does it work and when or why would the need to use one occur?

What is Function Recursion

## What is Memoization?

Memoization is a technique used in web development to speed up the execution of functions by caching the results of expensive function calls and returning the cached result when the same inputs occur again. The concept is very similar to caching on the server but done at a function level.

## Why Use Memoization?

Memoization is used to improve the performance of your code by reducing the number of times a function needs to execute. By caching the result of a function call, memoization can eliminate the need to perform complex calculations or expensive database queries every time a function is called with the same inputs.

T﻿he key here is to understand that the inputs to the function must match exactly for the function to use the memoized results instead of executing the function logic in its entirety again.

## How to Implement Memoization

To implement memoization, you need to create a cache that will store the results of function calls. How this is done depends on your technology stack and whether you have access to services like Redis for external caching of data.

At a base level, you can use an object or a Map to store the cached results. When a function is called, you check the cache to see if the result for the given inputs has already been computed. If it has, you return the cached result. If it hasn't, you compute the result and store it in the object or Map before returning it.

Here's an example of how to implement memoization in TypeScript:

```
const memoize = <T extends (...args: any[]) => any>(fn: T): T => {
  // Set up the cache map
  const cache = new Map();
  return ((...args: Parameters<T>): ReturnType<T> => {
    // Check if the key has already been cached and return the result if found
    const key = JSON.stringify(args);
    if (cache.has(key)) {
      return cache.get(key);
    }
    // If not found, execute the memoized function cache and return the result
    const result = fn(...args);
    cache.set(key, result);
    return result;
  }) as T;
};
```

I﻿n this example, the memoize function receives another function as its only argument. This function is the one that is complex or time-consuming that you want to cache the results from.

T﻿he memoize function then checks the cache map object to see if the complex function has been called before with the same set of arguments. If it has, the result of the function execution with those arguments is returned immediately.

I﻿f the key is not found, the memoize function then executes the complex function, caches the result and returns the result.

## When to Use Memoization?

1. C﻿aching Database Queries\
   I﻿f you have a function in your API logic that executes frequently with the same filter parameters, it may be worth memoizing the results so that the API does not need to make unnecessary requests to the database for the same data sets.
2. R﻿educing CPU Consumption\
   I﻿f the function is very CPU intensive to complete or long-running that affects other parts of your application, it would be sensible to memoize it.
3. I﻿mproving Network Performance\
   If the application makes many requests to a 3rd-party API, but with the same parameters, memoizing the results from the API will help reduce the number of API requests as well as speed up the application.

Memoization is a term you will come across at some stage when reading about frontend frameworks, libraries and in various packages you may need to use. This post will explain what memoization is, why use memoization and how to implement memoization.

What is Memoization?

## W﻿hat is Web Server Caching?

Web server caching is the storage of frequently accessed data in a secondary, temporary location to reduce the overall load on a web server. Caching allows data to be served directly from memory which can be faster and more efficient than making multiple connections to the actual database.

## W﻿hy use Caching?

T﻿he basic premise is that a user makes a request from a web app that interacts with an API and a database. The first time the user makes the request, the data retrieved by the API is inserted into a cache store. Each time the user then makes the same request again, the API retrieves the data from the cache store instead of executing the full logic of connecting to the database, retrieving the required data and applying any additional business logic. This reduces the load on the web server and database.

F﻿or heavily used apps, caching can have many benefits beyond performance. Reducing the data egress of the app will reduce costs (depending on the app architecture), and reduce compute power required by the web server (again reducing costs).

T﻿he type of data that might be cached could be: 

* The product catalogue on an e-commerce store The products offered remain static mostly, only the stock availability will change and would need to be handled separately.
* Database query results. Frequently executed database queries could be cached if the result set is static, perhaps if the values for a dropdown are fed from a data table.
* User Sessions. Caching is used to help manage user session data, such as login information, shopping cart contents or persisting user-defined settings for an app.

## H﻿ow to Configure Web Server Caching

T﻿here are a few different ways that a cache store can be configured. In today's technology environment, there is a multitude of Cache-as-a-service providers that can greatly reduce the complexity of implementing a caching system.

T﻿wo of the more popular cache store technologies are [Redis](https://redis.io/) and [MemCached](https://memcached.org/). Both of these technologies are supported by the main cloud providers:

* Amazon ElastiCache: A fully managed in-memory data store service offered by Amazon Web Services (AWS). Amazon ElastiCache supports both Redis and Memcached, and offers features such as backup and restore, automatic failover, and data encryption.
* Google Cloud Memorystore: A fully managed Redis service offered by Google Cloud. Google Cloud Memorystore provides a highly available and scalable Redis instance that is easy to set up and use.
* Microsoft Azure Cache for Redis: A fully managed Redis service offered by Microsoft Azure. Azure Cache for Redis provides high-performance and low-latency caching for web applications, and supports advanced features such as Redis clustering and data persistence.

### A﻿ NodeJs Example Cache Configuration

\*﻿This assumes you have a functional knowledge of NodeJs and Express.

A﻿fter setting up a Redis instance with a cloud provider of your choice, we need to configure our nodeJs Express app:

```typescript
// Import the required npm packages 
import express from 'express';
import { createClient } from 'redis';

// Create the app and redis client
const app = express();
const client = createClient({
  host: '<URL TO THE CLOUD REDIS INSTANCE>',
  port: 6379 // Default Redispor. Change as requierd.
});
// Connection and Error event listeners for the Redis instance
client.on('connect', function() {
  console.log('Redis client connected');
});

client.on('error', function (err) {
  console.log('Something went wrong ' + err);
});

// Middleware to check cache first
const checkCache = (req, res, next) => {
  const { id } = req.params;

  client.get(id, (err, data) => {
    if (err) throw err;

    if (data !== null) {
      res.send(JSON.parse(data));
    } else {
      next();
    }
  });
};

// API endpoint with caching
app.get('/product/:id', checkCache, (req, res) => {
  const { id } = req.params;

  // Query database for product with given ID
  const product = { id, name: "Example Product", price: 9.99 };

  // Store product in cache for next request
  client.set(id, JSON.stringify(product), {TTL: 3600 });

  res.send(product);
});

app.listen(3000, () => console.log('Server running on port 3000'));

```

I﻿n this express app the Redis library is imported and used to create a connection to the cloud Redis instance.

T﻿hen, a middleware is set up that checks the Redis store for an object using the given id. If the Redis store does contain the required data for the given id, then the actual endpoint logic is bypassed and the data is returned immediately to the user/client.

I﻿n the actual endpoint/product/:id, the product is retrieved from the 'database' and put into the cache. This will only execute if the data does not exist in the Redis cache store.

I﻿n this example, the cache entry has a 'time-to-live' value. This basically puts an expiration date on the data in the Redis store. When this expiration is reached, the data is automatically removed. The next request to the API for that product id will need to be retrieved from the database and put into the cache store again.

Web server caching is the storage of frequently accessed data in a secondary, temporary location to reduce the overall load on a web server. Caching allows data to be served directly from memory which can be faster and more efficient than making multiple connections to the actual database.

What is Server Caching and When to Use Caching

The Partial type in Typescript is a built in type that provides some very useful functionality to us to help manipulate other user-defined types while we are developing our app.

Eseentially, what the Partial type does is provide a wrapper for any other interface or type that is defined in our app and makes all of the properties of that interface or type optional.

This means we can create an object that is of a type or interface, but does not necessarily contain values for all of the properties defined in the type or interface.

```typescript
// Interface definition of a User where all properties are required
interface User {
    id: number;
    firstname: string;
    lastname: string;
    email: string;
    country: string;
}

/* 
A valid user variable that has 'incomplete' properties
This will not result in your IDE presenting typescript errors to you indicating
that properties are missing
*/
Partial<User> user = {
    firstname: 'James',
    lastname: 'Bond',
    country: 'England'
}
```

While this may initially sound like a bad idea, given that types and interfaces are designed to help us ensure that our objects are complete with values we expect, the Partial type is very useful for certain use cases.

The most obvious use case is when updating a database entity. Your app may allow a user to update their details, but not all of them - perhaps the email address cannot be changed.

In this case, you could define a second interface for the update model that excludes the email property, or you can define your code to use a Partial User that does not enfore the existence of the email property. 

In this update case, you can still enforce the requirement of the Id to be provided (as the id is needed to find the entity to update) by requiring it as a separate function parameter:

```typescript
async updateUser(id: number, Partial<User> user) => {
    await database.execute(...);
}
```

The Partial type works by taking the interface or type provided to it and evaluating the property names. It then ensures that any property provided when defining a partial variable is in that list of property names. This ensures that new or erroneous properties cannot be included. It also removes the mandatory requirement as defined in the original interface or type:

```typescript
/**
 * Make all properties in T optional
 */
 type Partial<T> = {
  [A in keyof T]?: T[A];
};

// From our example above
type UserKeys = keyof User;
// Returns: 'id' | 'firstname' | 'lastname' | 'email' | 'country'
// The A in keyof T then checks whether any property we provided is in the above list.
```

The Partial type in Typescript is a built in type that provides some very useful functionality to us to help manipulate other user-defined types while we are developing our app

How to Authenticate with Facebook using OAuth2 and React

Using Regex to Add Spaces Before Capital Letters in a String

What is Function Recursion

What is Memoization?

What is Server Caching and When to Use Caching

What is the Partial Type in Typescript