JavaScript Interview Questions(3)

柔光的暖阳◎ 2024-03-26 21:29 62阅读 0赞

## 1.How to write a comment in JavaScript? ##

There are two types of comments in JavaScript.

*  `Single Line Comment`: It is represented by `//`(double forward slash)
 *  `Multi-Line Comment`: Slash represents it with asterisk symbol as`/* write comment here */`

## 2.How to create a function in JavaScript? ##

> JavaScript Function Syntax

function functionName([arg1, arg2, ...argN]){
          
     //code to be executed  
    }

> JavaScript Function Arguments

> Function with Return Value

> JavaScript Function Object

*  In JavaScript, the purpose of `Function constructor` is to `create a new Function object`.
 *  It executes the `code globally`.
 *  However, if we call the constructor directly, a function is created `dynamically`but in an unsecured way.  
    **Syntax**

new Function ([arg1[, arg2[, ....argn]],] functionBody)

**Parameter**

*  arg1, arg2, … , argn - It represents the argument used by function.
 *  functionBody - It represents the function definition.

## 3. What are the different data types present in JavaScript? ##

JavaScript provides different data types to hold different types of values.  
There are two types of data types in JavaScript.

*  `Primitive data type`
 *  `Non-primitive (reference) data type`

> JavaScript primitive data types

![在这里插入图片描述][c4d8ce09f5ab4c9a929c64c87ac61e55.png]

> JavaScript non-primitive data types  
> ![在这里插入图片描述][4168915778144ff99bced157410ff283.png]

## 4.What is the difference between == and ===? ##

The `==` operator checks equality only whereas `===`checks equality, and data type, i.e., a value must be of the same type.

## 5.How to write HTML code dynamically using JavaScript? ##

*  The `innerHTML` property is used to write the HTML code `using JavaScript dynamically`

document.getElementById('mylocation').innerHTML="<h2>This is heading using JavaScript</h2>";

## 6.How to write normal text code using JavaScript dynamically? ##

*  The `innerText`property can be used to `write the dynamic text on the html document`. Here, text will not be interpreted as html text but a normal text.
 *  It is used mostly in the web pages to generate the `dynamic content` such as `writing the validation message, password strength`etc.

![在这里插入图片描述][e32a09ef19a340898d9e8ce3eb4ed2d3.png]

## 7.How to create objects in JavaScript? ##

*  `A javaScript object` is `an entity having state and behavior` (properties and method). For example: car, pen, bike, chair, glass, keyboard, monitor etc.
 *  JavaScript is `an object-based language`. Everything is an object in JavaScript.
 *  JavaScript is `template based not class based`. Here, we don’t create class to get the object. But, we direct create objects.
 *  There are 3 ways to create objects.
    
     *  `By object literal`
     *  `By creating instance of Object directly (using new keyword)`
     *  `By using an object constructor (using new keyword)`

> 1.  JavaScript Object by object literal  
>     **syntax**

object={
        property1:value1,property2:value2.....propertyN:valueN}

102 Shyam Kumar 40000

> 1.  By creating instance of Object

var objectname=new Object();

Here, new keyword is used to create object.

101 Ravi 50000

> 1.  By using an Object constructor

103 Vimal Jaiswal 30000

> Defining method in JavaScript Object

103 Sonoo Jaiswal 30000
    103 Sonoo Jaiswal 45000

## 8.How to create an array in JavaScript? ##

There are 3 ways to create an array in JavaScript.

*  `By array literal`
 *  `By creating an instance of Array`
 *  `By using an Array constructor`

> 1.  JavaScript array literal

syntax:

var arrayname=[value1,value2.....valueN];

> 1.  JavaScript Array directly (new keyword)

**syntax:**

var arrayname=new Array();

Arun
    Varun
    John

> 1.  JavaScript array constructor (new keyword)

you need to create instance of array by passing arguments in constructor so that `we don't have to provide value explicitly`.

Jai
    Vijay
    Smith

## 9.What does the isNaN() function? ##

*  The `isNan()`function `returns true` if the variable value is not a number.

## 10.What is the output of 10+20+“30” in JavaScript? ##

3030 because 10+20 will be 30. If there is numeric value before and after +, it treats as binary + (arithmetic operator).

3030

[c4d8ce09f5ab4c9a929c64c87ac61e55.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/e8d6eb653e81465db756c964475204fa.png
[4168915778144ff99bced157410ff283.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/fa326f32bc694505b31014dd6584544f.png
[e32a09ef19a340898d9e8ce3eb4ed2d3.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/25/515aca0ccf4947ccbbfc37d6fd59448b.png