Must Read Interview Questions on JavaScript

Must Read Interview questions on JavaScript

Interview Questions on JavaScript

Q1. What is JavaScript or JS?

Answer

JavaScript is a client-side programming language of the Web. The majority of modern websites and web applications make use of JavaScript in the HTML code. It is supported by all web browsers – Chrome, Mozilla, Netespace, etc.

JavaScript helps developers to create HTML pages more dynamic and interactive. JavaScript is a high-level, dynamic, untyped interpreted programming language that is well-suited to object-oriented and functional programming styles. Interview Questions on JavaScript

JavaScript derives its syntax from Java.

Q2. What are the important features of JavaScript?

Answer:

Following are important high-level features of JavaScript:

  • JavaScript is simple, lightweight and interpreted programming language.
  • JavaScript is cross-platform that can be executed on any platform and web browser.
  • JavaScript is Object Oriented. Interview Questions on JavaScript
  • JavaScript is Case-Sensitive
  • Client-side JavaScript exists to turn static HTML documents into interactive web applications

Q3. What is ECMAScript?

Answer:

ECMAScript is the original official name of the JavaScript programming language.

Also, read the following interview guides: [Interview Questions on JavaScript]

Q4. List some advantages of Javascript?

Answer:

  1. Cross-Platform Support – The Most important advantage of JavaScript is support for Cross-Platform
  2. Interactive User Interface.
  3. Rich Interfaces – Drag and Drop functionality or Slider adds rich user experience to websites
  4. Common code – across all browsers.
  5. In-built Functions – JavaScript provides an in-built set of common functions to perform basic operations, input, dates, drop-down list, etc. Interview Questions on JavaScript

Q5. Differentiate between Core Java vs JavaScript?

Answer:

JavaScript is completely different from the Java programming language.  JavaScript has grown as a general purpose web scripting language. JavaScript was created at Netscape in the early days of the Web, and technically, “Java-
Script” is a trademark licensed from Sun Microsystems (now Oracle) used to describe.

Netscape’s (now Mozilla’s) implementation of the language. Interview Questions on JavaScript

Netscape submitted the language for standardization to ECMA—the European Computer Manufacturer’s Association
and because of trademark issues, the standardized version of the language was stuck with the awkward name “ECMAScript.”

JavaScript provides a minimal set of Library APIS to achieve basic tasks text, arrays, dates, etc. The JavaScript programming language, developed by Netscape, Inc., is not part of the Java platform. JavaScript cannot be used to create standalone applications, it can be embedded into HTML code only.

JavaScript code runs in a client web browser and Java code execute in JVM. Java code needs to be first compiled while JS is just plain text.

Q6. List the common data types in JavaScript?

Answer:

Computer programs work by manipulating values, such as the number 3.14 or the text “Hi JavaScript”. These kinds of values that can be represented and manipulated in a programming language are known as types, and one of the most fundamental characteristics of a programming language is the set of types it supports. Interview Questions on JavaScript

JavaScript types can be divided into two categories: primitive types and object types. JavaScript’s primitive types include numbers, strings of text (known as strings), and Boolean truth values (known as booleans). A significant portion of this chapter is dedicated to a detailed explanation of the numeric (§3.1) and string (§3.2) types in JavaScript.

Object – Any JavaScript value that is not a number, a string, a boolean, or null or undefined is an object.

Q7. How to declare and access a variable in JavaScript?

Answer:

Before using a variable in a JavaScript program, you should first declare it. Variables are declared with the var keyword, like this:
    var age;
    var protocol;

You can also declare multiple variables with the same var keyword:
    var i, sum;

And you can combine variable declaration with variable initialization:
    var message = “hello”;
    var i = 0, j = 0, k = 0;

If you don’t specify an initial value for a variable with the var statement, the variable is declared, but its value is undefined until your code stores a value into it.

Q8. How do you define a function in JavaScript?

Answer:

A function is a block of JavaScript code that is defined once but may be executed, or invoked, any number of times. You may already be familiar with the concept of a function under a name such as a subroutine or procedure.

Example Defining JavaScript functions
// Function definition
function Sum() {
    var a = 10, b = 20;

   var sum = a+b;

   return sum;   
}

Q9. What are multiple ways to use JavaScript code in HTML?

Answer:

1. JavaScript code can be defined in an HTML script tag

<script>
   function clickMe() {
    document.getElementById(“txtName”).style.fontSize = “27px”;
    document.getElementById(“txtName”).style.color = “green”;
   document.getElementById(“txtName”).style.backgroundColor = “yellow”;
  }
</script>

<button type=”button” onclick=”clickMe()”>Let Me Check!</button>

Note: Script tag can be used in head and body sections of HTML page.

2. External JS file

JavScript code can be placed in a separate .js file and then included in the head section of every page where it is required: Interview Questions on JavaScript

Using this mechanism you can use the same common code on multiple web pages.

How to use external JavaScript file?
<html>
<head>
<script type = “text/javascript” src = “myJS.js” ></script>
</head>

<body>
…….
</body>
</html>

Q10. Differentiate between DOM vs BOM?

Answer:

DOM: 

DOM stands for Document Object Model. Every web browser window, tab, and the frame is represented by a Window object. Every Window object has a document property that refers to a Document object. The Document object represents the content of the window, and it is the subject of this chapter. The Document object does not stand alone, however. 

It is the central object in a larger API, known as the Document Object Model, or
DOM, for representing and manipulating document content.

Interview questions on javascript
Interview questions on javascript

BOM:
BOM stands for Browser Object Model which consists of browser-related information. JavaScript BOM contains browser components – history, navigator, location, screen, etc. Interview Questions on JavaScript

Read Laravel Tutorials:

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Further Reading:[Interview Questions on JavaScript]

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