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Javascript Interview Questions and Answers

Pratik Bandal

About Book

Javascript Interview Questions and Answers is extremely useful for beginners and professionals who are preparing for interview of Javascript or web technologies. This book covers interview questions of Javascript which is required form UI and full stack development. It is also recommended to go through other web technologies like HTML, CSS as it is difficult to cover so many technologies in this small book.

The book will prepare you for interview as well as refining your knowledge of Javascript and will make you ready for working in industry.

For any positive or negative feedback regarding this book, kindly reach me at pratikbandal007@gmail.com

About Author

I am Pratik Bandal currently working in a big multinational company and have over 6 years of experience in software industry. I have done B.E. (E&TC) and Post graduate diploma in Advanced Computing. I have experience in different domains like healthcare, payment and banking sectors.

But on top of all, I am developer like you all guys doing an 8 hour job. Writing is something I do extra and I love doing it. No one is perfect and holds true for me as well. Without all you guys I am not an author.

Writing an interview question book is a really great deal of responsibility. But huge natural variations in interview are something difficult to cover in this small book.

Contents

Fundamentals

---

What is Javascript?

Javascript is basically scripting language used to make web pages more interactive as it can be inserted into HTML.

Javascript is understood by all modern web browsers.

What are features of Javascript?

Input validation : Javascript allows you to validate user input before sending it to server for backend operations.

Control over browser : Javascript gives more control over browser due to which you can change the background colour of this page as well as the text on the browser's status bar.

Detect browser and OS : Javascript enables you to detect users browser and OS due to which you can perform platform dependant operations.

Handling date and time : Javascript enables you to write code based users date and time, it also enables you to capture users date and time as user and server may be in different time zone.

Generating HTML on fly : Javascript enables you to dynamically generate HTML.

What are advantages of Javascript?

Faster speed : JavaScript is fast because it run immediately within the client-side browser. Javascript is not dependant on network unless backend data is required to be processed. Need to compile Javascript on the clientside as it is interpreted directly by web browsers.

Interoperability : Javascript can be inserted into web page regardless of extension. Within other languages such as Perl and PHP it can be used inside the script.

Rich interfaces : Javascript has vast libraries like (charts, drag and drop, sliders etc.) which enables you to provide attractive look to your website.

Reduction in server load : Since Javascript is client-side scripting language it reduces load on website servers as many operations can be performed at client-side which reduces load on server and enables it serve to more users.

What are disadvantages of Javascript?

Client-side security : JavaScript code executes in users computer hence in some cases it can be manipulated for malicious purpose.

Browser support : JavaScript is sometimes interpreted differently by different browsers.

What is difference between Javascript and ECMAScript?

JavaScript is a scripting language that has been formed by keeping ECMAScript specification at its core.

ECMAScript is nothing but a standard or specification defined in order to create different scripting languages and one of them is JavaScript.

Javascript, Jscript and ActionScript are few scripting languages that follow ECMAScript specifications.

Who developed Javascript?

JavaScript was created in 1995 by Brendan Eich during his time at Netscape Communications. It was inspired by Java, Scheme and Self.

How to insert Javascript in Web page?

You can use tag in html. tag has type attribute which defined which code is there inside the script tag.

You can use element in web pages in following ways:

• In head element

  • In body element

    • As an external script file

      To use Javascript as a scripting language for web pages in or you can define type as text/javascript.

      e.g.

      Sometime you may need to use same Javascript code in several web pages, in such cases you can store Javascript code in external file and save file as .js file.

      Then this script can be made available to web page using src attribute of tag

      e.g.

      What are advantages of using external javascript?

      Placing JavaScript code in external js files has few advantages over inline scripts:

      Segregating HTML and JavaScript code helps to manage the code base better.

      To improve development output designers can work along with coders in parallel without code conflicts.

      This approach also works well with modern source code version control systems like GIT and SVN.

      Each of these files can maintain history.

      Segregating HTML and JavaScript makes code as well as HTML is easily readable.

      Segregated external JavaScript files are cached by browsers and can speed up page load times

      These small js files can be minified to reduce the size and make it not readable by humans, using Google closure or YUI Compressor or other.

      Many popular JavaScript libraries are available as hosted on content delivery networks (cdn) and you can simply point to them using the URL in the src, this avoids copying the js file to local folder.

      Using external Js you can take benifits of advanced tools such as RequireJS or CommonJS to load these scripts logically and modularly

      Javascript is case sensitive language?

      Yes, Javascript is case sensitive scripting language. Variables, functions, keywords must have consistent casing otherwise it will not be recognized by Javascript and will generate error.

      e.g.

      var pratik;

      var praTik;

      In above case pratik and praTik will be considered as different variables.

      Is Semicolon compulsory in Javascript at end of the statement?

      No, it is not necessary to use semicolon at end of the statement still it will be considered as valid statement.

      What are different data types in Javascript?

      Below are basic data types in Javascript:

      Primitive Data Types:

      • Number: Represent numeric values, both integer and float.
      • String: Sequence of characters are represented using String.
      • Boolean: Represent Boolean value, true or false.
      • Undefined: Represent undefined value.
      • Null: Represent null.

      Non-Primitive Data Types:

      • Object: Represent more complex data structure.
      • Array: Represent group of elements.
      • RegExp: Represent regular expression.

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