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Post By AdminLast Updated At 2020-06-15
JavaScript Interview Questions

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  1. What is JavaScript?

JavaScript is a client-side as well as server side scripting language that can be inserted into HTML pages and is understood by web browsers. JavaScript is also an Object based Programming language.

  1. What is the difference between JavaScript and Java?

Java is an Entire programming language. In Distinction, JavaScript is a coded program that can be popularized to HTML pages. These 2 languages are not at all inter-dependent and are designed for different intent. Java is an object-oriented programming (or) structured programming languages like C++ or C whereas JavaScript is a client-side scripting language. - What is Java?

  1. What are JavaScript Data Types?

 The JavaScript Data types

  • Number
  • String
  • Boolean
  • Object
  • Undefined
  1. What are the Different Types of Scope Chain Available in JavaScript?

If we check in the program, every local scope has a connection with one or more scope in their back which forms a chain. This chain goes on until it met with the global scope which is the root of this hierarchy. As global scope doesn't have a parent, so it is on the top of the chain. This is known as the scope chain. The scope chain in JavaScript is basically used to resolve the values of the variable. Without this, it is difficult for a JavaScript to choose a certain value for a variable if there are many variables defined at different scopes.

  1. How do we add JavaScript onto a web page?

 There are more ways for adding JavaScript on a web page, but there are two ways which are commonly used by developers If your script code is very short and only for a single page, then following ways are the best:

You can place the tag inside the  element.Page Title
  1. What is the use of is NaN function?

 Is Nan function returns true if the argument is not a number otherwise it is false?

  1. Explain MUL Function In JavaScript?

 MUL means simple multiplication of numbers. It is a technique in which you pass a one value as an argument in a function and that function returns another function to which you pass the second value and the process go on. For example: x*y*z can be representing as:

Function mul (x) { Return function (y) { // anonymous function   Return function (z) {// anonymous function     Return x * y * z;    };  };}
  1. What are The Different Types of Errors in JavaScript?

There are 3 types of errors in JavaScript

Load time errors: Errors which come up when loading a web page like irregular syntax errors are known as Load-time errors and it generates the errors dynamically.

Run time errors: Errors that come due to the exploitation of the command inside the HTML language.

Logical Errors: These are the errors that occur due to the bad logic performed on a function which is having a different operation.

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  1. How to create arrays in JavaScript?

There are 2 ways to create array in JavaScript like other languages:

a) The first way to create array

var names = new Array();Add Elements in Arraynames[0] = "phani";names[1] = " aravindh";names[2] = "Nikhil";

b) This is the second way:

Var names = new Array ("Vikas", "Ashish", "Nikhil");

  1. List of Design Patterns in JavaScript?

The design pattern is a general Durable solution to a frequently Occurring problem in software design. Some of the design patterns are:

Creational design pattern: These patterns dealt with the mechanism of object creation which optimize object creation with the basic approach.

Structural design pattern: these patterns deal with different classes and objects to provide new functionality.

Behavioral Patterns: These patterns are to improve communication between objects and to recognize patterns.

Concurrency design patterns: These patterns handle with multi-thread programming paradigms.

Architectural design patterns: These patterns used to deal with architectural designs.

  1. What is the use of Math Object in JavaScript?

The math object provides you properties and methods for mathematical constants and functions.

Var x = Math.PI; // Returns PIVar y = Math.sqrt(16); // Returns the square root of 16Var z = Math.sin(90); Returns the sine of 90
  1. What is the difference between ViewState and SessionState?

'ViewState' is Exact to a page in a session.

'SessionState' is Exact to user-specific data that can be accessed across all pages in the web application.

  1. Does JavaScript support automatic type conversion?

Yes JavaScript does Encourages automatic type conversion, it is the frequent way of type conversion used by JavaScript developers

  1. What are all the looping structures in JavaScript?

They Are 3 looping structures in JavaScript:

  • For
  • While
  • do-while loops
  1. Explain how to read and write a file using JavaScript?

   There are 2 ways to read and write a file using JavaScript

  • Using JavaScript extensions
  • Using a web page and Active X objects
  1. Explain Promise In JavaScript?

A promise is an object in JavaScript which is used to produce a value that may give result in the future. The value can be resolved value or it can be a reason which tells why the value is not resolved.

A promise can be of three states:

Fulfilled: The operation is completed and the promise has a specific value.

Rejected: The operation is failed and promise has a reason which shows why the operation failed.

Pending: The operation is not fulfilled or rejected, means it has not completed yet.

  1. What is called Variable typing in JavaScript?

 Variable typing is used to assign a number to a variable and the similar variable can be assigned to a string.

i = 10;i = "string";
  1. Consider the following statements and tell what would be the output of the logs statements?
 var price1 = 10;var price2 = 10;Var price3 = new Number ('10'); // A complex numeric object because new was used.log(price1 === price2);log(price1 === price3);
  1. How to Add New Property in Existing Function JavaScript?

It is easy to add an advanced property in an existing function by just giving value to the existing function it. For example, let us have an Actual object person, to give new property check the below code:

Person. Country= “India”;The advanced property “country” has added to the object person.
  1. What is the definition of prompt box?

The Input Give by any user in the JavaScript is entered with the help of a prompt box. While putting progressive the data or the input, the prompt box allows the user to do so with the help of a text box. To include the number, label box is also used.

  1. What is an undefined value in JavaScript?
  • Undefined value means the:
  • Variable used in the code doesn’t exist
  • Variable is not assigned to any value
  • The property doesn’t exist
  1. Define event bubbling?

JavaScript Enters DOM elements to be nested inside each other. Once choice of the, if the handler of the child is clicked, the handler of the parent will also work as if it were clicked too.

  1. JavaScript Code Implementation?

There are 3 ways to add JavaScript commands to your Web Pages:

  • Embedding code
  • Inline code
  • External file
  1. What are JavaScript Cookies?

A function that is stated without any named identifier is known as an anonymous function. In general, an unidentified function

Is inaccessible after its declaration. Unidentified function declaration:
Var wcg = function () {Alert (’I am unidentified’);};wcg ();
  1. What is 'this' keyword in JavaScript?

 'This' keyword refers to the object from where it was called.

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