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AJAX Materials-Free Download





Brief about Ajax.

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.

Differentiate between Synchronous and Asynchronous Ajax requests.

Synchronous Ajax requests – In this, the script stops and waits for the server to reply before continuing. In 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.

List some advantages and disadvantages of using Ajax.

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 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.

What is XMLHttpRequest object in Ajax? How can you XMLHttpRequest Object?

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.

How to cancel the current request in Ajax?

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.

How to send an Ajax request in JavaScript?

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.

Explain Fetch API in JavaScript.

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.

Explain limitations of Ajax.

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 user request and server response – needs 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.

What are the advantages of Ajax?

Following are the advantages of Ajax:

• Bandwidth utilization – It saves memory when the data is fetched from the same page.

• More interactive

• Speeder retrieval of data

What are the disadvantages of Ajax?

Following are the disadvantages of Ajax:

1. AJAX is dependent on Javascript. If there is some Javascript problem with the browser or in the OS, Ajax will not support

2. Ajax can be problematic in Search engines as it uses Javascript for most of its parts.

3. Source code written in AJAX is easily human readable. There will be some security issues in Ajax.

4. Debugging is difficult

5. Increases size of the requests

6. Slow and unreliable network connection.

7. Problem with browser back button when using AJAX enabled pages.

What is update panel?

Update panel is a server control used to update the specified portion of a web page. Script Manager needs to be used whenever update panel is used. Using update panel, user cannot handle outside controls.

Which are the two methods used for cross domain Ajax calls?

There are two methods used to transfer data between the two more more security domains:

• CORS – Cross Origin Resource Sharing and it works with the HTTP web browsers

• JSONP – JSON with Padding which works with the HTTP GET and on legacy browsers

What are all the technologies used by Ajax?

AJAX uses following technologies:

• JavaScript

• XMLHttpRequest

• Document Object Model (DOM)

• Extensible HTML (XHTML)

• Cascading Style Sheets (CSS)

What are all the features of Ajax?

Following are the features of Ajax and they are as follows:

• Live data binding

• Client-side template rendering

• Declarative instantiation of client components

• Observer pattern on JavaScript objects and arrays

• Invoking ADO.NET data services and data contexts

• DataView control

What is JSON in Ajax?

JSON is abbreviated as JavaScript Object Notation.

JSON is a safe and reliable data interchange format in JavaScript, which is easy to understand for both users and machines.

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