Intro to Backend Development with NodeJS

What is HTTP?

HTTP (Hypertext Transfer Protocol) involves communication between a client (typically a web browser) and a server (where a website or web service is hosted). The key components of this communication are HTTP requests and HTTP responses, and they serve different purposes:

HTTP Request

An HTTP request is sent from the client (e.g., your web browser) to the server.

It specifies the action the client wants the server to perform.

It typically includes:

• The HTTP method (GET, POST, PUT, DELETE, etc.) indicating the type of action.
• The URL (Uniform Resource Locator) or endpoint that identifies the resource on the server.
• Headers providing additional information about the request.
• Optionally, a request body containing data to be sent to the server, typically used in POST or PUT requests.

The client initiates the request, and it is processed by the server.

HTTP Response

An HTTP response is sent from the server to the client in response to an HTTP request. It contains the information or data requested by the client or indicates the outcome of the requested action.

It typically includes:

• A status code (e.g., 200 for success, 404 for “Not Found,” 500 for “Internal Server Error”) indicating the result of the request.
• Headers providing metadata about the response, such as content type or length.
• Optionally, a response body containing the actual data or content requested by the client. The server generates the response and sends it back to the client as a reply to the client’s request.

In summary, an HTTP request is a message sent from the client to the server to initiate an action or request data, while an HTTP response is the server’s reply to that request, containing the requested data or information about the outcome of the request. These two components are fundamental to the way information is exchanged between clients and servers on the web.

HTTP Status Codes

HTTP status codes are three-digit numbers that indicate the outcome of an HTTP request made by a client (like a web browser) to a server. They provide crucial information about whether the request was successful, encountered an error, or requires further action. Here are some common types of status codes and why they are important:

• 2xx (Successful): These codes indicate that the request was successful and the server has fulfilled it.

  • 200 OK: The most common success code, indicating the request was successful and the server is returning the requested data.

• 3xx (Redirection): These codes indicate that the client needs to take further action to complete the request.

  • 301 Moved Permanently: The requested resource has been permanently moved to a different URL.
  • 302 Found (or 307 Temporary Redirect): The requested resource is temporarily located at a different URL.

• 4xx (Client Errors): These codes indicate that there was an issue with the client’s request.

  • 400 Bad Request: The request was malformed or contained invalid syntax.
  • 404 Not Found: The requested resource was not found on the server.
  • 403 Forbidden: The server understands the request, but it refuses to fulfill it due to permission or authentication issues.

• 5xx (Server Errors): These codes indicate that there was an issue on the server’s side while processing the request.

  • 500 Internal Server Error: A generic error message indicating something went wrong on the server, often due to a misconfiguration or code issue.
  • 502 Bad Gateway: The server, while acting as a gateway, received an invalid response from the upstream server.

Why They Are Important:

• Debugging: Status codes help developers diagnose issues when something goes wrong. For example, a 404 status code tells them that a resource wasn’t found, while a 500 code suggests a server-side problem.

• User Experience: For end-users, status codes can provide feedback. A 404 status, for instance, tells them the page they’re looking for doesn’t exist, while a 200 code indicates a successful page load.

• SEO: Search engines use status codes to understand the state of web pages. Properly handling codes like 301 for permanent redirects can improve search engine rankings.

• Efficiency: Clients and servers use status codes to efficiently handle requests and responses. Knowing a request was successful (2xx) allows the client to proceed, while errors (4xx or 5xx) signal the need for action or troubleshooting.

In summary, HTTP status codes are vital for communication between clients and servers on the web. They provide clear and standardized information about the outcome of HTTP requests, enabling efficient problem-solving and enhancing the user experience.

HTTP Methods

HTTP methods are often used to perform CRUD (Create, Read, Update, Delete) operations on resources.

Here’s an explanation of HTTP methods that includes CRUD operations, example URLs, JSON data, and the difference between requests and responses for non-technical users:

GET:

Purpose: To retrieve data (Read) from a web server.

Example URL: https://example.com/api/posts/1

Example JSON Response:

    {
      "id": 1,
      "title": "Hello World",
      "content": "This is a sample post."
    }

Explanation: When you visit a webpage like https://example.com/api/posts/1, your browser sends a GET request to the server, asking for information. The server responds with the requested data in a JSON format, which your browser then displays.

POST:

Purpose: To create new data (Create) on a web server or submit data for processing. Example URL: https://example.com/api/posts Example JSON Request:

{
    "title": "New Post",
    "content": "This is a new post."
}

Explanation: When you submit a form on a website, like creating a new post at https://example.com/api/posts, your browser sends a POST request to the server with the data you entered. The server processes this data and responds, confirming that the new data has been created.

PUT

Purpose: To update existing data (Update) on a web server or create it if it doesn’t exist.

Example URL: https://example.com/api/posts/1

Example JSON Request:

{
    "title": "Updated Post",
    "content": "This post has been updated."
}

Explanation: When you edit an existing post, like at https://example.com/api/posts/1, your browser sends a PUT request to the server with the updated data. The server receives this request, identifies the resource you want to update, and responds to confirm the changes.

DELETE

Purpose: To remove data (Delete) from a web server.

Example URL: https://example.com/api/posts/1

Example JSON Response:

    {
        "message": "Post with ID 1 has been deleted."
    }

Explanation: When you delete a post, like at https://example.com/api/posts/1, your browser sends a DELETE request to the server. The server processes the request, removes the specified resource, and responds with a confirmation message.

In these examples, the request is what your browser sends to the server to ask for something or make changes (GET, POST, PUT, DELETE), and the response is what the server sends back to confirm or provide the requested information.

Asynchrnous Programming vs. Syncrhonous Programming

Asynchronous programming and synchronous programming are two different approaches to handling tasks and operations in a computer program. They differ in how they manage the flow of execution and handle potentially time-consuming or blocking operations, such as I/O operations or network requests.

In synchronous programming, tasks are executed sequentially, one after the other. When a function or task is invoked, the program waits for it to complete before moving on to the next task. If a task takes a long time to complete, it can block the entire program, making it unresponsive and inefficient. Synchronous code is often easier to read and reason about because the flow of execution is straightforward.

function synchronousFunction() {
    console.log("Task 1");
    console.log("Task 2");
}

synchronousFunction();

In this example, “Task 2” will not be executed until “Task 1” has completed.

In asynchronous programming, tasks are initiated, but the program doesn’t wait for them to complete. Instead, it continues executing other tasks. Asynchronous operations are often used for tasks that can take a variable amount of time, such as reading from a file, making network requests, or waiting for user input. Callbacks, Promises, and async/await are common mechanisms for handling asynchronous code, making it more manageable and less error-prone.

Example in JavaScript using Promises:

    function asynchronousFunction() {
        console.log("Task 1");
        setTimeout(function() {
            console.log("Task 2");
        }, 2000); // Simulating a delay of 2 seconds
    }

    asynchronousFunction();

In this example, “Task 2” is scheduled to run asynchronously after a 2-second delay, while the program continues executing other tasks.

Key differences between asynchronous and synchronous programming:

• Blocking vs. Non-blocking: Synchronous code blocks the execution of the program until a task is complete, while asynchronous code allows the program to continue executing other tasks without waiting for completion.

• Concurrency: Asynchronous code can improve concurrency and responsiveness in applications, as it allows multiple tasks to run concurrently without blocking the main thread.

• Complexity: Asynchronous code can be more complex due to callback nesting or Promise chaining. However, modern async/await syntax has made asynchronous code easier to read and maintain.

• Error handling: Asynchronous code often requires special attention to error handling, as errors that occur in asynchronous tasks may not be immediately apparent.

In summary, asynchronous programming is a technique used to manage tasks that can take time to complete without blocking the program’s execution. It allows for better resource utilization and responsiveness in applications, especially in scenarios involving I/O operations or network requests.

Hello Word Program with NodeJS and Express

const express = require('express');
const bodyParser = require('body-parser'); // We use body-parser to parse JSON data from POST requests
const app = express();
const port = 3000;

// Middleware to parse JSON data from requests
app.use(bodyParser.json());

// Define a route that responds to GET requests
app.get('/', (req, res) => {
  res.status(200).send('Hello, World!');
});

// Define a route that responds to POST requests
app.post('/create', (req, res) => {
  // Read data from the request body
  const requestData = req.body;

  // Process the data (you can customize this part)
  const responseData = {
    message: 'Data received successfully!',
    data: requestData,
  };

  // Send a 201 (Created) status code with the response
  res.status(201).json(responseData);
});

// Start the server
app.listen(port, () => {
  console.log(`Server is running on port ${port}`);
});