Ajax Interview Questions

Ajax is considered to be a developer’s best friend because it offers several benefits to him such as updating the web page without reloading the entire page, requesting data from the server and also sending data to the server. AJAX is the acronym for Asynchronous JavaScript and XML. It is a new technique to communicate to and from a server/ database without completely refreshing the page. It creates faster, interactive, better web applications with help of CSS, XML, HTML, and JavaScript.

Synchronous Ajax requests: In this, the script stops and waits for the server to reply before continuing. In the web application world, one has to happen after the other, i.e. the interaction between the customer and the server is synchronous. Synchronous is not recommended as it blocks/hangs the page until the response is received from the server.

Asynchronous Ajax requests handle the reply as and when it comes and allows the page to continue to be processed. Under Asynchronous, if there is any problem in the request it can be modified and recovered. The request doesn’t block the client as the browser is responsive. The user can perform other operations as well.

Ajax is a very easy concept if one has a sound knowledge of JavaScript. It uses JavaScript functions to call methods from a web service. It has certain advantages-

• Speed- Ajax reduces the server traffic and also the time consumption on the server and client side.
• Ajax is very responsive and fast, data can be transferred at a time.
• XMLHttpRequest plays a significant role in Ajax. It is a special JavaScript object that calls asynchronous HTTP request to the server for transferring data.
• One of the biggest advantages of using Ajax as forms are common elements in the web page. Ajax gives options for validation and much more.
• One doesn’t have to completely reload the page.

There are some disadvantages attached to Ajax. They are-

• Search engines would not be able to index Ajax applications so Ajax maybe a mistake.
• Anyone can have access to the code of Ajax and can view source it.
• ActiveX requests are enabled only in internet explorer and other new browsers.

There are total 5 ready state in Ajax:

The XMLHttpRequest objects are used to exchange data with a server. It is an API whose methods transfer between a web browser and a web server. In XHR, it’s not necessary that data have to be in form of XML. It can be JSON or HTML. XHR can be used with protocols other than HTTP.

XMLHttpRequest is any developers kit because it has the option to update the page without reloading the entire page. You can request data from the server and also send data to the server in the background.

Current request in AJAX is cancelled when the user performs an action which sets of an Ajax request. This can be depicted with the help of auto-complete functionality for a search box where users can be helped with related search terms based on their current input, by making an AJAX request each time they pass a key in search field. The user types faster than the Ajax request and you would want to abort any non-finished requests, before starting the next one.

HTTP Requests are created with the help of XMLHttpRequest objects. It facilitates the transfer of data between client and server which happens via request and response. In XMLHttpRequest, you can perform the same function plus you can grab data from URL without having to refresh the page. AJAX lets you perform actions without reloading the entire page. The following steps tell how to call AJAX-

• Create an XMLHttpRequest object.
• Open the request with open method.
• Now, send the request with the send method.

var xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
     document.getElementById("demo").innerHTML = this.responseText;
    }
  };
  xhttp.open("GET", "get_results.php", true);
  xhttp.send();

Fetch API uses to request and response objects that can be used in future whenever needed. It provides an interface for fetching resources. Fetch API uses promises that enable cleaner API. Cache API or other similar things handles the request and responses that might require you to generate your own responses programmatically.

Thus, you can now crack your interview and work as a developer in one of your dream companies by preparing from these set of question and answers to be technically sound.

1) Browser Integration

The dynamically created page does not register itself with the browser history engine, so triggering the “Back” function of the users’ browser might not bring the desired result.

2) Response-time Concerns

Network latency – or the interval between the user request and server response – need to be considered carefully during Ajax development.

3) Search Engine Optimization (SEO)

Websites that use Ajax to load data which should be indexed by search engines must be careful to provide equivalent Sitemaps data at a public, linked URL that the search engine can read, as search engines do not generally execute the JavaScript code required for Ajax functionality.

4) Reliance on JavaScript

Ajax relies on JavaScript, which is often implemented differently by different browsers or versions of a particular browser. Because of this, sites that use JavaScript may need to be tested in multiple browsers to check for compatibility issues.

The Process of retrieving data from a server to obtain near-live data regularly is called AJAX polling.