ajax-summary.md

AJAX (Asynchronous JavaScript and XML) Cheat Sheet:

1. AJAX Basics:

• AJAX allows you to update parts of a web page without reloading the entire page.
• It uses JavaScript to send and receive data from a server asynchronously.
• AJAX can be used to retrieve data from a server, send data to a server, and update parts of a web page dynamically.

2. XMLHttpRequest Object:

• The XMLHttpRequest object is the core of AJAX.
• It allows you to send HTTP requests to a server and handle the response.
• Create a new XMLHttpRequest object: var xhttp = new XMLHttpRequest();

3. AJAX Workflow:

• Create an XMLHttpRequest object.
• Define a callback function to handle the server response.
• Open a connection to the server using the open() method.
• Send the request to the server using the send() method.
• Handle the server response in the callback function.

4. AJAX Methods:

• open(method, url, async): Specifies the type of request, URL, and whether the request should be asynchronous.
• send(data): Sends the request to the server. Optional data can be included.
• abort(): Cancels the current request.
• setRequestHeader(header, value): Sets the value of an HTTP request header.

5. AJAX Events:

• onreadystatechange: Triggered whenever the readyState property changes.
• onload: Triggered when the request has been completed successfully.
• onerror: Triggered if an error occurs during the request.

6. AJAX Ready States:

• 0: Request not initialized.
• 1: Server connection established.
• 2: Request received.
• 3: Processing request.
• 4: Request finished and response is ready.

7. AJAX Response Handling:

• Use the responseText property to get the response as a string.
• Use the responseXML property to get the response as an XML document.
• Use the status property to get the HTTP status code of the response.
• Use the statusText property to get the status text of the response.

8. AJAX Cross-Origin Requests:

• AJAX requests are subject to the same-origin policy, which restricts requests to the same domain.
• To make cross-origin requests, the server must include the appropriate CORS (Cross-Origin Resource Sharing) headers.
• Alternatively, you can use JSONP (JSON with Padding) or a proxy server to overcome cross-origin restrictions.

9. AJAX Libraries/Frameworks:

• jQuery: A popular JavaScript library that simplifies AJAX requests with its $.ajax() method.
• Axios: A lightweight HTTP client library that supports AJAX requests in both browsers and Node.js.
• Fetch API: A modern browser API for making AJAX requests, providing a more powerful and flexible alternative to XMLHttpRequest.

Remember to always handle errors, sanitize user input, and secure your AJAX requests to prevent security vulnerabilities.