Five Ajax Interview Questions Every Developer Must Know

ajax interview questionsAjax stands for asynchronous JavaScript and XML. Ajax is a group of related technologies that are used to display information asynchronously – that is, without reloading a page – to a user. For example, you may use Ajax to show new posts or recent comments on a web page without reloading it, which can dramatically improve user experience. Ajax was at the forefront of the Web 2.0 revolution of the mid-2000s and is widely used in websites today.

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Ajax is not a single programming language and does not owe its invention to any individual or group. Ajax came about as a result of experiments by a number of different organizations, including Microsoft and Google. “Ajax: A New Approach to Web Applications”, an article by user-experience designer Jesse James Garrett, was influential in popularizing Ajax among web developers (all would-be Ajax developers are advised to read the original article, which can be found here). By 2006, the W3C attempted to create a web standard for Ajax with the release of the first draft specification for XHMLHttpRequest.

Since Ajax does not specify any particular technology, job interviews for Ajax frequently focus on the underlying technologies (including XML, DOM, JavaScript) and how they interact both among themselves, and with page-level elements (i.e. HTML and CSS). Below, we’ll take a look at some of the most common questions asked in Ajax interviews:

1. Explain Some Common Security Issues with Ajax.

An Ajax call acts as a conduit between the user and the server. All data collected by the Ajax call is transmitted to the server in plain text. This data may often contain sensitive information such as usernames, passwords, email addresses, etc. Since the data is sent in plain text, it is extremely vulnerable to hacker attacks.

Hackers can also use Ajax to insert malicious scripts in a webpage and monitor user activity. Further, Ajax fundamentally encourages developers to create more than one server-side pages. The larger the number of server-side pages, the more entry points hackers have to gain access to secure data.

2. Which Side Controls an Ajax Interaction – Server Side or Client Side?

Establishing control in any Ajax interaction is not a black and white process. Control can either be server-side, or use a mix of server-side and client-side controllers.

  • Client + Server-Side Control: In this structure, one may use allocate all presentation related control to JavaScript on the client side. This includes manipulating pages, rendering data, processing events, etc. The server-side, meanwhile, handles things such as updating model data and delivering it to the client. This is a more secure architecture as the server does not have in-depth knowledge of data being presented on the client-side.
  • Central Server-Side Control: In this architecture, control stays with the server-side which pushes updates to the client DOM through JavaScript. It is important to ensure that the server-side stays in sync with the client side when using this control method.

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3. If You Had to Create Your Own Ajax Functionality from Scratch, What Technologies Would You Use?

This question is essentially asking us about the technologies that make up Ajax. Knowing what we know about Ajax, if we had to build Ajax functionality from scratch, we would have to learn the following technologies/languages:

  • JavaScript: JavaScript is used to present all data on the client-side. It is an essential component of any Ajax functionality. JavaScript is used to record events such as a mouse click, a key press, etc. and display data pulled from the server-side. Mastering JavaScript is essential to mastering Ajax.
  • DOM: DOM or Document Object Model, is a cross-platform convention or API used for interacting with an object in a XML or HTML page.
  • CSS: CSS or Cascading Style Sheets is a web standard used for styling and presenting data on a web page.
  • DHTML: DHTML refers to the combination of JavaScript, DOM and CSS. This is the technology that is used to interact with web pages in real-time and is the foundation of Ajax.

Besides these technologies, a strong understanding of how HTTP requests work, especially XMLHttpRequests, is also crucial for building your own Ajax functionality. You can learn how to use Ajax with this course on building a fast loading, SEO friendly Ajax website.

4. What Are Some Disadvantages of Using Ajax on a Web Page?

  • Security: As mentioned above, Ajax transmits data  from the client to the server-side in plain text. This makes Ajax applications vulnerable to hackers.
  • Search Engine Indexing: All Ajax interactions utilize JavaScript. However, Google’s web crawlers cannot execute JavaScript code. This means that any Ajax app cannot be indexed by Google’s bots, negatively affecting a website’s search engine visibility.
  • Development Time: Since Ajax basically involves learning and using a number of different technologies, development time for an Ajax application can be much longer than for an app written in a comparable language.
  • User-Experience: In an Ajax application, data is loaded asynchronously from the server to the client. Since there is no page-refresh, there is no browsing history. This means that the back/forward buttons in a browser are rendered useless, which can affect user-experience. It is possible to mitigate this problem using the Really Simple History library.
  • Accessibility Issues: As mentioned above, Ajax essentially disables the back/forward buttons. This can affect a website’s accessibility. It also cannot work on browsers with JavaScript disabled (~5% of browsers). Some mobile/tablet browsers also have trouble dealing with Ajax.

5. List Some Common Ajax Frameworks.

A framework or library is a set of technologies that make it easier to develop Ajax applications. Ajax frameworks are essentially JavaScript libraries that speed up development time. Some of the more common frameworks are:

  • Dojo Toolkit: Dojo Toolkit is a modular JavaScript toolkit distributed under an open-source license. This toolkit has been in development since 2004 and includes a variety of UI effects, widget APIs, drag and drop AISs etc. Dojo is the most popular Ajax framework and is used in a huge number of applications.
  • MooTools: The MooTools framework is one of the more popular JavaScript toolkits that is used primarily for creating visual effects such as sliders, slideshows, etc.
  • Prototype: The Prototype toolkit emphasizes visuals effects, animations and interactions. It’s a lightweight toolkit that is great for rapid iteration. It also supports Rico and which add additional visual effects capabilities.
  • YUI: YUI or Yahoo User Interface library is an open source JavaScript framework that is used to make interactive applications.
  • Spry: The Spry framework was developed by Adobe and is distributed under the BSD license. It consists of animation and visual effects components (Spry Effects), a data binding component (Spry Data), and a framework to crate widgets (Spry Widgets).
  • Google Web Toolkit (GWT): The GWT enables developers to create rich Ajax applications using Java. GWT takes all the Java code and compiles it to JavaScript. It also has an exhaustive set of debugging tools, making it perfect for testing applications.

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What Ajax interview questions were you asked in your interview? Share in the comments section below!