JavaScript interview questions are gathered for people who are applying for JS jobs. JavaScript was created by Brendan Eich in 1995 to give web pages a little more pep than the <blink> tag could provide. Today it has far more powerful uses and companies like Google and Facebook use JavaScript to build complex desktop-like web applications. With the launch of Node.js, It has also become one of the most popular languages for building server-side software. The following are the interview questions of JavaScript:
Table of Contents
JavaScript is a client-side as well as a 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
JavaScript Interview Questions
Java is a complete programming language. In contrast, JavaScript is a coded program that can be introduced to HTML pages. These two languages are not at all inter-dependent and are designed for different intent. Java is an object-oriented programming (OOPS) or structured programming languages like C++ or C whereas JavaScript is a client-side scripting language.
JavaScript Interview Questions
Following are the JavaScript Data types:
isNan function returns true if the argument is not a number otherwise it is false.
JavaScript is faster. JavaScript is a client-side language and thus it does not need the assistance of the webserver to execute. On the other hand, ASP is a server-side language and hence is always slower than JavaScript. Javascript now is also a server-side language (Node JS).
JavaScript Interview Questions
Negative Infinity is a number in JavaScript which can be derived by dividing negative number by zero.
Breaking within a string statement can be done by the use of a backslash, ‘\’, at the end of the first line
Example:
document.write("This is \a program");
And if you change to a new line when not within a string statement, then javaScript ignores break in line.
Example:
var x=1, y=2,z=x+y;
The above code is perfectly fine, though not advisable as it hampers debugging.
Netscape is a software company who developed JavaScript.
JavaScript Interview Questions
Undeclared variables are those that do not exist in a program and are not declared. If the program tries to read the value of an undeclared variable, then a runtime error is encountered.
JavaScript Interview Questions
Undefined variables are those that are declared in the program but have not been given any value. If the program tries to read the value of an undefined variable, an undefined value is returned.
<html> <head> <title>t1</title> <script type="text/javascript"> function addNode() { var newP = document.createElement("p"); var textNode = document.createTextNode(" This is a new text node"); newP.appendChild(textNode); document.getElementById("firstP").appendChild(newP); } </script> </head> <body> <p id="firstP">firstP<p> </body> </html>
Global variables are those that are available throughout the length of the code, that is, these have no scope. The var keyword is used to declare a local variable or object. If the var keyword is omitted, a global variable is declared.
Example:
// Declare a global globalVariable = "Test";
The problems that are faced by using global variables are the clash of variable names of local and global scope. Also, it is difficult to debug and test the code that relies on global variables.
A prompt box is a box which allows the user to enter input by providing a text box. Label and box will be provided to enter the text or number.
You may be interested in reading an article on Authentication.
‘This’ keyword refers to the object from where it was called.
Timers are used to execute a piece of code at a set time or also to repeat the code in a given interval of time. This is done by using the functions setTimeout, setInterval and clearInterval.
JavaScript Interview Questions
The setTimeout(function, delay) function is used to start a timer that calls a particular function after the mentioned delay. The setInterval(function, delay) function is used to repeatedly execute the given function in the mentioned delay and only halts when cancelled. The clearInterval(id) function instructs the timer to stop.
Timers are operated within a single thread, and thus events might queue up, waiting to be executed.
// for Single line comments and
/* Multi
Line
Comment
*/
‘ViewState’ is specific to a page in a session.
‘SessionState’ is specific to user specific data that can be accessed across all pages in the web application.
=== is called as strict equality operator which returns true when the two operands are having the same value without any type conversion.
To submit a form using JavaScript use document.form[0].submit();
Yes JavaScript does support automatic type conversion, it is the common way of type conversion used by JavaScript developers
It can be done in the following way:
document.getElementById("myText").style.fontSize = "20?;
or
document.getElementById("myText").className = "anyclass";
There are two ways to read and write a file using JavaScript
Following are looping structures in Javascript:
Undefined value means the
Variable used in the code doesn’t exist
Variable is not assigned to any value
Property doesn’t exist
JavaScript Interview Questions
Void(0) is used to prevent the page from refreshing and parameter “zero” is passed while calling.
Void(0) is used to call another method without refreshing the page.
JavaScript Interview Questions
The following code has to be inserted to achieve the desired effect:
<script language="JavaScript" type="text/javascript" > <!-- location.href="http://newhost/newpath/newfile.html"; //--> </script>
All variables in the JavaScript are object data types.
JavaScript Interview Questions
An alert box displays only one button which is the OK button.
But a Confirmation box displays two buttons namely OK and cancel.
Escape characters (Backslash) is used when working with special characters like single quotes, double quotes, apostrophes and ampersands. Place backslash before the characters to make it display.
Example:
document.write "I m a "good" boy" document.write "I m a \"good\" boy"
Cookies are the small test files stored in a computer and it gets created when the user visits the websites to store information that they need. Example could be User Name details and shopping cart information from the previous visits.
JavaScript Interview Questions
The pop() method is similar as the shift() method but the difference is that the Shift method works at the start of the array. Also the pop() method take the last element off of the given array and returns it. The array on which is called is then altered.
Example:
var cloths = ["Shirt", "Pant", "TShirt"];cloths.pop(); //Now cloth becomes Shirt,Pant
No. JavaScript does not have a concept level scope. The variable declared inside the function has scope inside the function.
If you use innerHTML in JavaScript the disadvantage is
Content is replaced everywhere
We cannot use like “appending to innerHTML“
Even if you use +=like “innerHTML = innerHTML + ‘html’” still the old content is replaced by html
The entire innerHTML content is re-parsed and build into elements, therefore its much slower
The innerHTML does not provide validation and therefore we can potentially insert valid and broken HTML in the document and break it
JavaScript Interview Questions
Break statement exits from the current loop.
Continue statement continues with next statement of the loop.
They are as –
Primitive types are number and Boolean data types. Reference types are more complex types like strings and dates.
Generic objects can be created as:
var I = new object();
‘Typeof’ is an operator which is used to return a string description of the type of a variable.
Try… Catch—finally is used to handle exceptions in the JavaScript
Try{Code}Catch(exp){Code to throw an exception}Finally{Code runs either it finishes successfully or after catch}
JavaScript Interview Questions
document.write(“Welcome”) is used to print the text – Welcome in the screen.
Blur function is used to remove the focus from the specified object.
Variable typing is used to assign a number to a variable and then assign string to the same variable. Example is as follows:
i= 8;i=”john”;
The ‘Navigator.appversion’ is used to find the name of the operating system in the client machine.
There are three types of errors:
JavaScript Interview Questions
The push method is used to add or append one or more elements to the end of an Array. Using this method, we can append multiple elements by passing multiple arguments
Unshift method is like push method which works at the beginning of the array. This method is used to prepend one or more elements to the beginning of the array.
Both are almost similar. JavaScript is developed by Netscape and Jscript was developed by Microsoft.
Strict mode is a way to introduce better error-checking into your code.
When you use strict mode, you cannot use implicitly declared variables, or assign a value to a read-only property, or add a property to an object that is not extensible.
You can enable strict mode by adding “use strict” at the beginning of a file, a program, or a function.
A prompt box is a box which allows the user to enter input by providing a text box. The prompt() method displays a dialogue box that prompts the visitor for input. A prompt box is often used if you want the user to input a value before entering a page. When a prompt box pops up, the user will have to click either “OK” or “Cancel” to proceed after entering an input value.
JavaScript Interview Questions
NaN is a short form of Not a Number. Since NaN always compares unequal to any number, including NaN, it is usually used to indicate an error condition for a function that should return a valid number. When a string or something else is being converted into a number and that cannot be done, then we get to see NaN.
JavaScript Interview Questions
Undeclared variables are those that do not exist in a program and are not declared. If the program tries to read the value of an undeclared variable, then a runtime error is encountered. Undefined variables are those that are declared in the program but have not been given any value. If the program tries to read the value of an undefined variable, an undefined value is returned.
If you need any backlink or you are interested in placing an ad on this page, you may contact at itsaareez1@gmail.com
Sponsored by WebSoft IT Development Solutions (Private) Limited
NGINX Server Nginx, a popular open-source web server, excels at handling high traffic websites efficiently.… Read More
In the realm of web hosting, choosing the right web server is paramount. It acts… Read More
Are indispensable for ensuring smooth, precise linear motion in many industrial applications. Whether in robotics,… Read More
Cyber attacks are becoming more frequent, complex, and damaging. They can disrupt critical operations and… Read More
With the rise of new threats and the increasing complexity of IT environments, organizations need… Read More
1. Introduction In software design, managing complex systems can be challenging. The Facade Design Pattern… Read More