jQuery - How jQuery AJAX Works Under the Hood

jQuery AJAX is a mechanism that allows web pages to communicate with a server in the background without reloading the page. Instead of submitting a form traditionally, AJAX sends an asynchronous HTTP request and processes the response dynamically, giving users a smoother and faster experience.

Creation of the AJAX Request
When an AJAX method is triggered, jQuery first collects the request details such as URL, HTTP method, data and headers. Internally, jQuery prepares these options and validates them before sending the request. This preparation step ensures the request follows standard HTTP rules.

Use of XMLHttpRequest Object
Behind the scenes, jQuery relies on the browser’s native XMLHttpRequest (XHR) object. jQuery creates and configures this object to open a connection with the server. It sets request headers, attaches data and defines how the response should be handled once it arrives.

Asynchronous Execution
AJAX requests run asynchronously by default. This means the browser does not stop user interaction while waiting for the server response. jQuery registers callback functions that are executed only when the server responds, keeping the page responsive during the process.

Response Handling and Callbacks
Once the server sends back a response, the XHR object notifies jQuery. jQuery then parses the response based on its type, such as JSON, HTML or text. After parsing, it triggers success, error or complete handlers so developers can react appropriately.

Error Detection and Status Codes
jQuery checks HTTP status codes to determine whether a request succeeded or failed. Responses in the 200 range are treated as successful, while client or server errors trigger error callbacks. This abstraction saves developers from manually checking low-level response details.

Why jQuery AJAX Feels Simple
Although AJAX involves complex browser APIs, jQuery hides most of that complexity. Developers interact with a clean and readable interface while jQuery handles request creation, execution, error handling and response parsing internally. This makes AJAX easier to use and less error-prone, especially for beginners.