JavaScript Interview Questions and Answers

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Top and Most frequently asked JavaScript Interview Questions and Answers in the industry are provided here. We ensure that we provide latest and standard JavaScript Interview Questions and Answers in this article.

Let’s get started with JavaScript Interview Questions :

Is it mandatory to use any IDE or Development Environment for Coding in JavaScript ?

We don’t need to use any IDE. By default, JavaScript is running in all devices. Best example is Browser.

Are JavaScript and Java almost same languages ?

JavaScript and Java are completely different languages. This includes both design and concept.

What is the specification and Official language name given to JavaScript ?

ECMA is the specification given to JavaScript and Official name is termed as ECMAScript.

What are the ways to Load JavaScript in a HTML Document ?

There are two ways to load JavaScript in a HTML document and they are shown below :

  1. Inline Script
  2. External Script
Example of Inline Script :
<script>
var jsInterview = 'Javascript Interview Questions and Answers';
console.log(jsInterview);
</script>
Example of External Script :
<script src="externalFile.js"></script>

and externalFile.js contains following code:

var jsInterview = 'Javascript Interview Questions and Answers';
console.log(jsInterview);

Both approaches will give the same result and there is no much difference.

Which approach is best to load JavaScript and Why ?

Best Approach is using External Files. Below are the reasons :

  • By using External files HTML and CSS is separated from JavaScript code which makes developer job easy to maintain the code.
  • External files can be cacheable and they can increase the page load time.

What is the difference between Declaration and Definition in JavaScript ?

Declaration Example :
var temp;
Definition Example :
temp = 5;

To make you understand better, see the below code :

var temp; // declaration
temp = 5; // definition
var abc = 3; //declaration and definition included

Explain Type Conversion in JavaScript with example ?

For example, we have two variables one with integer value and one with string value. Now, if we add them JavaScript will output a String value as follows :

var intValue = 50;
var strValue = " JavaScript Interview Questions"
var mixedValue = intValue + strValue;
console.log(mixedValue); --> Returns the value "50 JavaScript Interview Questions"

So, Basically JavaScript don’t expect for external type casting. It will automatically assume and convert the value into any type.

However, a point to be noted here is that, If we add a number and string we get result as a String but if we subtract then we get an Integer value.

What is the difference between “==” and “===” ?

“==” converts the both operands to same type before comparing which is known as Type Coercion.

“===” doesn’t convert to same type before comparing.

In simpler words, “==” checks the value comparison but will not check type but “===” checks both value and type comparison.

What is Immediate Function in JavaScript ?

The Name itself tells us that a Function which is executed immediately after it is defined.

Immediate Function Syntax :
(function(){
    console.log('This is a Immediate Function');
}())

What are the differences between Call By Value and Call By Reference in JavaScript ?

Call By ValueCall By Reference
Actual value is not modified on changing dependent variable.Actual value is modified on changing dependent variable.
Actual and Dependent variable are present in different memory locations.Actual and Dependent variable are present in same memory location.
In case of function, changes in variable passed will not affect the actual value.In case of function, changes in variable passed will affect the actual value.
Call By Value Vs Call By Reference (JavaScript Interview Questions)

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