Categories of JavaScript Interview Questions
Ans: JavaScript is a scripting language. It is different from Java language. It is an object-based, lightweight, and cross-platform. It is widely used for client-side validation.
Ans: 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 it is provided by Microsoft.
Ans: A simple example of JavaScript hello world is given below. You need to place it inside the body tag of HTML.
<script type="text/javascript">
document.write("JavaScript Hello World!");
</script> Ans: I am assuming that js file name is message.js, place the following script tag inside the head tag.
<script type="text/javascript" src="message.js"></script>
Ans: Yes.
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Ans: BOM stands for Browser Object Model. It provides interaction with the browser. The default object of the browser is the window.
Ans: 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.
Ans: The window object is automatically created by the browser that represents a window of a browser.
It is used to display the popup dialog box such as the alert dialog box, confirm dialog box, input dialog box, etc.
Ans: The history object of the 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()
history.forward()
history.go(number): number may be positive for forward, negative for backward.
Ans: There are two types of comments in JavaScript.
Single Line Comment: It is represented by // (double forward slash)
Multi-Line Comment: It is represented by a slash with asterisk symbol as /* write comment here */
Ans: To create a function in JavaScript, follow the following syntax.
function function_name(){
//function body
}
Ans: There are two types of data types in JavaScript:
Primitive Data Types
Non-primitive Data Types
Ans: The == operator checks equality only whereas === checks equality and data type i.e. value must be of the same type.
Ans: The innerHTML property is used to write the HTML code using JavaScript dynamically. Let's see a simple example:
document.getElementById('mylocation').innerHTML="<h2>This is heading using JavaScript</h2>";
Ans: The innerText property is used to write the simple text using JavaScript dynamically. Let's see a simple example:
document.getElementById('mylocation').innerText="This is text using JavaScript";
Ans: There are 3 ways to create objects in JavaScript.
By object literal
By creating an instance of Object
By Object Constructor
Let's see a simple code to create an object using an object literal.
emp={id:102,name:"Rahul Kumar",salary:50000}
Check Out Java Script Tutorial
Ans: There are 3 ways to create an array in JavaScript.
By array literal
By creating an instance of Array
By using an Array constructor
Let's see a simple code to create an array using object literal.
var emp=["Shyam","Vimal","Ratan"];
Ans: The isNan() function returns true if the variable value is not a number.
Ans: 3030 because 10+20 will be 30. If there is a numeric value before and after +, it is treated is binary + (arithmetic operator).
Ans: 102030 because after a string all the + will be treated as a string concatenation operator (not binary +).
Ans: Client-side JavaScript comprises the basic language and predefined objects which are relevant to running javascript in a browser. The client-side JavaScript is embedded directly in the HTML pages. This script is interpreted by the browser at run time.
Server-side JavaScript also resembles like client-side javascript. It has a relevant javascript which is to run in a server. The server-side JavaScript are deployed only after compilation.
Ans: The storage of cookies on the hard disk depends on OS and the browser.
The Netscape navigator on Windows uses cookies.txt file that contains all the cookies. The path is : c:Program FilesNetscapeUsersusernamecookies.txt
The Internet Explorer stores the cookies on a file username@website.txt. The path is: c:WindowsCookiesusername@Website.txt.
Ans: The original name was Mocha, a name chosen by Marc Andreessen, founder of Netscape. In September of 1995, the name was changed to LiveScript. In December 1995, after receiving a trademark license from Sun, the name JavaScript was adopted.
Ans: Undefined value: A value that is not defined and has no keyword is known as an undefined value. For example:
int number;//Here, the number has an undefined value.
Null value: A value that is explicitly specified by the keyword "null" is known as null value. For example:
String str=null;//Here, str has a null value.
Ans: The cursor can be set to wait in JavaScript by using the property "cursor". The following example illustrates the usage:
<script>
window.document.body.style.cursor = "wait";
</script>
Ans: var myArray = [[[]]];
Three-dimensional array.
Ans: No, Java and JavaScript are the two different languages. Java is a robust, secured, and object-oriented programming language whereas JavaScript is a client-side scripting language with some limitations.
Ans: Negative Infinity is a number in JavaScript which can be derived by dividing negative numbers by zero.
Ans: "View state" is specific to a page in a session whereas "Session state" is specific to a user or browser that can be accessed across all pages in the web application.
Ans: Alert Box
Confirm Box
Prompt Box
Ans: The navigator.appVersion string can be used to detect the operating system on the client machine.
Ans:
Let's see the JavaScript code to submit the form on clicking the link.
<form name="myform" action="index.php">
Search: <input type='text' name='query' />
<a href="javascript: submitform()">Search</a>
</form>
<script type="text/javascript">
function submitform()
{
document.myform.submit();
}
</script>
Ans:
Yes, because it doesn't require a web server's support for execution.
Ans:
<script type="text/javascript">
document.body.bgColor="pink";
</script>
Ans: By the help of try/catch block, we can handle exceptions in JavaScript. JavaScript supports try, catch, finally, and throw keywords for exception handling.
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