19 JavaScript Interview Questions and Answers

This Javascript interview questions and answers tutorial is meant to get you acquainted with the JavaScript programmer interview. We will provide you with the key concepts you are likely to meet in any interview office you visit. JavaScript is a standard tool used today in the web design environment. You will find its all-purpose core integrated into Netscape, Internet Explorer among other web browsers available today.

Go through this article for 20 Javascript interview questions to help you with your interview.

Question 1: What is JavaScript?

This is the most obvious question interviewers will ask on the JavaScript subject.
JavaScript is a client and server-side scripting language that has object-oriented capabilities and can be input into HTML and interpreted by the web browsers.

Question 2: What is the difference between Java and JavaScript?

Java is an entirely conventional programming language whereas JavaScript is a coded program that is inserted into HTML pages to communicate with web browsers.
Java is an Object Oriented programming language that is structured in nature whereas JavaScript is a client-side scripting language that is unstructured in nature.
JavaScript can also be used as a complimentary language for Java and HTML during web design and other commercial applications.

Question 3: What are the JavaScript features?

? The browser support function: this enables the users to access Flash content without having to install flash plugins on the browser.
? It is applicable both to the client and server side: JavaScript allows the user to format their web page with a variety of effects. On the server side JavaScript can be used in the creation of web scripts, hence allowing the customization of tasks in a web browser.
? JavaScript is a functional programming language: Just like any other language, data types, functions and operations can be assigned to a variable. In addition to that, a function can be integrated with another function as a parameter, hence returning other functions. This is exactly how a functional programming style operates.
? Support for objects: JavaScript supports several object oriented concepts just like other conventional OOPS like Java and still manages to remain simple to learn and work with.

Question 4: List the JavaScript types.

The JavaScript types available include Number, String, Boolean, function, object undefined and null.

Question 5: What is the major distinction between undeclared variables from the undefined variables?

Undeclared variables are variables that cannot be found within the program, and when the program attempts to read the undeclared variable, it returns a runtime error.
Undefined variables, on the other hand, are declared in the program, however, haven?t been assigned values. When the program attempts to read the value of an undefined variable, it returns an undefined value.

Question 6: What is closure in JavaScript language?

It is a function that is defined within another function that is usually referred to as the parent function. A closure has access to variables declared and defined in its parent function scope. It has access to variables in three ranges which are:

• Those declared in their own scope;
• Variables?declared in their parent function scope;
• And the ones declared in the global namespace.

Question 7: When using type of bar === ?object? to determine whether ?bar? is an object or not, what could be the potential danger?

Null in JavaScript is also considered an object. Therefore when using type of bar === ?object,? the code will log ‘true’ to the console as opposed to the expected false. You can solve this problem by also checking if ?bar? is null. For more details on that, visit?JavaTPoint’s Java static keyword page.

Question 8: Why is it important or rather significant to wrap the whole content of a JavaScript?

The wrapping technique helps create a closure around the entire contents of the record which will then create a private namespace. The importance of that is to avoid potential clashing of names between the varied Javascript libraries and modules.

This technique also serves in creating a shorter alias for the global variables. For instance, in the jQuery, the $ reference in a jQuery namespace can be disabled by the following function;

jQuery.noCnflict ()

Question 9: What is NaN? Give its type.

It is a property that represents a value which isn?t a number. When an operation cannot be executed perhaps for containing a non-numeric operand, a NaN value is returned. For instance, in a case where the operation involves diving a number by zero.

However, the data type of NaN is number despite being an acronym for ?not a number.’

Question 10: Briefly describe how to create an object in Javascript.

An object is created through the use of the object literal below;
Var emp = {
Name: ?Peter?,
Age: 15
};

Question 11: Define the global variables and show their declaration.

Global variables are variables that don?t have a scope meaning that they are found throughout the length of the code. The var function usually declares local variables within the entire body of the code; hence you can declare a global variable by omitting it. However, when declaring a global variable you risk experiencing clashing of names within local and global scopes.

Question 12: What is meant by a prompt box as a JavaScript tool?

It is a text box that provides a way of inputting data and also provides a label for the box.

Question 13: Is it possible to assign an anonymous function to a variable?

Yes, it is possible.

Question 14: What is the ?arguments object? in JavaScript?

Arguments object are variable arguments that represent the arguments that are sent to a function.

Question 15: Are there any naming conventions for Javascript?

Yes, one should not name their variables with any of the reserved keywords. For instance, the names used by break and Boolean variables aren?t valid.
The first character of the javascript variables should never be a numeral, which includes numbers from zero to nine.
The names are case sensitive. If you don?t observe that, they will be treated as two different variables.

Question 16: Is it possible to access cookies in Javascript?

Yes, Javascript can create, read, manipulate and remove cookies on the web page. It does that with the Document object property.

Question 17: What role does the Void (0) function play?

The function is used to invoke a new or different method without refreshing the page.

Question 18: What is the ?===? operator as used in JavaScript?

The operator is often referred to as the strict equality operator. It usually returns a true value if the two operands have the same value without a conversion in the type of either of the two. It is much stricter than the ?==? operator which only checks for the equality of values.

Question 19: How can one convert a string of any given base to an integer in JavaScript?

When converting numbers into different bases, the function parseInt () is usually employed. The operation considers the string to be converted as its initial parameter. The base of the string in question forms the second parameter.

Upon reading this article, you will realize that Javascript is also a functional, object-oriented programming language that can complement HTML and Java. The answers to these 20 javascript interview questions may not be perfect but are just a stepping stone for you into the JavaScript programming language. Therefore, you can provide suggestions or comments on these javascript interview questions based on your thoughts on the same.