JavaScript Interview Questions(2)

绝地灬酷狼 2023-09-25 18:50 42阅读 0赞

# 1. If we want to return the character from a specific index which method is used? #

*  The JavaScript string `charAt() method`is used to find out a char value present at the specified index.
 *  The index number starts from 0 and goes to n-1, where n is the length of the string.
 *  The index value can’t be a negative, greater than or equal to the length of the string.

var str="Javatpoint";    
    document.writeln(str.charAt(4));

# 2.What is the difference between JavaScript and JScript? #

*  Netscape provided `the JavaScript language`.
 *  Microsoft changed the name and called it `JScript` to avoid the trademark issue.
 *  In other words, you can say JScript is the same as JavaScript, but Microsoft provides it.

# 3.How to write a hello world example of JavaScript? #

*  The script tag specifies that we are using JavaScript.
 *  The `text/javascript` is the content type that provides information to the browser about the data.
 *  The `document.write()`function is used to display dynamic content through JavaScript.

# 4.What are the key differences between Java and JavaScript? / How is JavaScript different from Java? #

*  `JavaScript` is a `lightweight` programming language (most commonly known as scripting language) developed by Netscape, Inc.
 *  It is used to `make web pages interactive`. It is not a part of the Java platform.

<table> 
 <thead> 
  <tr> 
   <th>Java</th> 
   <th>JavaScript</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Java is a complete and <code>strongly typed programming language</code> used for <code>backend coding</code>. <br>In Java, variables must be declared first to use in the program, and the type of a variable is checked at compile-time.</td> 
   <td>JavaScript is a <code>weakly typed</code>, <code>lightweight programming language</code> (most commonly known as scripting language) and has more relaxed syntax and rules.</td> 
  </tr> 
  <tr> 
   <td>Java is an <code>object-oriented programming (OOPS) </code>language or structured programming languages such as C, C++, or .Net.</td> 
   <td>JavaScript is <code>a client-side scripting language</code>, and it doesn’t fully support the OOPS concept. It resides inside the <code>HTML documents</code> and is used to make web pages interactive (not achievable with simple HTML).</td> 
  </tr> 
  <tr> 
   <td>Java creates applications that can run in <code>any virtual machine (JVM) or browser</code>.</td> 
   <td>JavaScript code can run<code> only in the browser</code>, but it can now run on the server via Node.js.</td> 
  </tr> 
  <tr> 
   <td>The Java code needs to be <code>compiled</code>.</td> 
   <td>The JavaScript code <code>doesn't require to be complied</code>.</td> 
  </tr> 
  <tr> 
   <td>Java Objects are <code>class-based</code>. You can’t make any program in Java without creating a class.</td> 
   <td>JavaScript Objects are <code>prototype-based</code>.</td> 
  </tr> 
  <tr> 
   <td>Java is a Complete and Standalone language that can be used <code>in backend coding</code>.</td> 
   <td>JavaScript is assigned within a web page and integrates with its <code>HTML content</code>.</td> 
  </tr> 
  <tr> 
   <td>Java programs <code>consume more memory</code>.</td> 
   <td>JavaScript code is used in HTML web pages and requires <code>less memory</code>.</td> 
  </tr> 
  <tr> 
   <td>The file extension of the Java program is written as “.Java” and it translates source code into bytecodes which are then executed by JVM (Java Virtual Machine).</td> 
   <td>The JavaScript file extension is written as “.js” and <code>it is interpreted but not compiled</code>. Every browser has a JavaScript interpreter to execute the JS code.</td> 
  </tr> 
  <tr> 
   <td>Java supports <code>multithreading</code>.</td> 
   <td>JavaScript <code>doesn't support multithreading</code>.</td> 
  </tr> 
  <tr> 
   <td>Java uses<code> a thread-based approach to concurrency</code>.</td> 
   <td>JavaScript uses an <code>event-based approach to concurrency</code>.</td> 
  </tr> 
 </tbody> 
</table>

# 5.How to use external JavaScript file? #

# 6.Is JavaScript case sensitive language? #

Yes, JavaScript is a case `sensitive language`. For example:

Var msg = "JavaScript is a case-sensitive language"; //Here, var should be used to declare a variable  
    function display()   
    {
          
    document.writeln(msg); // It will not display the result.  
    }   
    display();

# 7.What is BOM? #

*  `BOM` stands for `Browser Object Model`.
 *  It provides interaction with the browser.
 *  The `default object` of a browser is a window.
 *  So, you can call all the functions of the window by specifying the window or directly.
 *  The window object provides various properties like document, history, screen, navigator, location, innerHeight, innerWidth

![在这里插入图片描述][042c7c6ae1084284a090efd7023e4392.png]

# 8.What is DOM? What is the use of document object? #

*  `DOM` stands for `Document Object Model`.
 *  `A document object`represents the `HTML document`.
 *  It can be used to `access and change the content of HTML.`

![在这里插入图片描述][3ca9b5ccb7364fa485cdf478063eff55.png]

<table> 
 <thead> 
  <tr> 
   <th>Method</th> 
   <th>Description</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>write(“string”)</td> 
   <td>writes the given string on the doucment.</td> 
  </tr> 
  <tr> 
   <td>writeln(“string”)</td> 
   <td>writes the given string on the doucment with newline character at the end.</td> 
  </tr> 
  <tr> 
   <td>getElementById()</td> 
   <td>returns the element having the given id value.</td> 
  </tr> 
  <tr> 
   <td>getElementsByName()</td> 
   <td>returns all the elements having the given name value.</td> 
  </tr> 
  <tr> 
   <td>getElementsByTagName()</td> 
   <td>returns all the elements having the given tag name.</td> 
  </tr> 
  <tr> 
   <td>getElementsByClassName()</td> 
   <td>returns all the elements having the given class name.</td> 
  </tr> 
 </tbody> 
</table>

![在这里插入图片描述][2b7d178916f4467088632a9d00b9c7d7.png]

# 9.What is the use of window object? #

*  `The window object` represents `a window in browser`.
 *  An object of window is created `automatically by the browser`.

<table> 
 <thead> 
  <tr> 
   <th>Method</th> 
   <th>Description</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>alert()</td> 
   <td>displays the alert box containing message with ok button.</td> 
  </tr> 
  <tr> 
   <td>confirm()</td> 
   <td>displays the confirm dialog box containing message with ok and cancel button.</td> 
  </tr> 
  <tr> 
   <td>prompt()</td> 
   <td>displays a dialog box to get input from the user.</td> 
  </tr> 
  <tr> 
   <td>open()</td> 
   <td>opens the new window.</td> 
  </tr> 
  <tr> 
   <td>close()</td> 
   <td>closes the current window.</td> 
  </tr> 
  <tr> 
   <td>setTimeout()</td> 
   <td>performs action after specified time like calling function, evaluating expressions etc.</td> 
  </tr> 
 </tbody> 
</table>

> Example of alert() in javascript

> Example of confirm() in javascript

> Example of prompt() in javascript

> Example of open() in javascript

> Example of setTimeout() in javascript

# 10. What is the use of history object? #

*  The history object of a browser can be used to switch to history pages such as back and forward from the current page or another page.
 *  There are three methods of history object.
    
     *  `history.back()` \- It loads the `previous page`.
     *  `history.forward()` \- It loads the `next page`.
     *  `history.go(number)` \- The number may be positive for forward, negative for backward. It loads the given page number.

history.back();//for previous page  
    history.forward();//for next page  
    history.go(2);//for next 2nd page  
    history.go(-2);//for previous 2nd page

[042c7c6ae1084284a090efd7023e4392.png]: https://img-blog.csdnimg.cn/042c7c6ae1084284a090efd7023e4392.png
[3ca9b5ccb7364fa485cdf478063eff55.png]: https://img-blog.csdnimg.cn/3ca9b5ccb7364fa485cdf478063eff55.png
[2b7d178916f4467088632a9d00b9c7d7.png]: https://img-blog.csdnimg.cn/2b7d178916f4467088632a9d00b9c7d7.png