Hello Guys! If you are looking for JavaScript Questions For Interview then you are on the right webpage. In this blog, we have shared 20+ JavaScript Question that are useful for Interview. The students who are learning JavaScript can check their level of learning by answering below questions. If you find this article useful then don’t forget to share with your friends.

What is JavaScript?

JavaScript is a client-side and server-side scripting language inserted into HTML pages and is understood by web browsers. JavaScript is also an Object-based Programming language

Enumerate the differences between Java and JavaScript?

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.

What is negative Infinity?

Negative Infinity is a number in JavaScript which can be derived by dividing negative number by zero.

Is it possible to break JavaScript Code into several lines?

Breaking within a string statement can be done by using a backslash, ‘\,’ at the end of the first line. eg: document. Write (“This is a program,”);

Which company developed JavaScript?

Netscape is the software company that developed JavaScript.

What are the data types supported by JavaScript?

The data types supported by JavaScript are: • Undefined, Boolean, String, Number, Object

What is the use of isNaN function?

isNan function returns true if the argument is not a number; otherwise, it is false.

Which is faster between JavaScript and an ASP script?

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 (nodejs).

What are undeclared and undefined variables?

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.

What is a prompt box?

A prompt box is a box that allows the user to enter input by providing a text box. A label and box will be provided to enter the text or number.

What is ‘this’ keyword in JavaScript?

‘This’ keyword refers to the object from where it was called.

What is the working of timers in JavaScript?

Timers are used to execute a piece of code at a set time or repeat the code in a given interval. This is done by using the functions setTimeout, setinterval, and clearinterval.

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 repeatedly executes the given function in the mentioned delay and only halts when canceled. 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.

Is JavaScript a case-sensitive language?

Yes, JavaScript is a case sensitive language. The language keywords, variables, function names, and any other identifiers must always be typed with a consistent capitalization of letters.

Which symbol is used for comments in Javascript?

// for Single line comments and 
/* Multi

What is === operator?

=== is called a strict equality operator, which returns true when the two operands have the same value without conversion.

Does JavaScript support automatic type conversion? Yes, JavaScript does support automatic type conversion. It is the common way of type conversion used by JavaScript developers

What are all the looping structures in JavaScript?

Following are looping structures in Javascript:

• For

• While

• Do-while loops

Does JavaScript support automatic type conversion?

It can be done in the following way:

document.getElementById("myText"). style. fontSize = "20";


document.getElementByld ("myText"). className = "anyclass";

Difference between “==” and “===”?

“==” checks only for equality in value, whereas “===” is a stricter equality test and returns false if either the value or the type of the two variables are different.

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