javascript Interview Questions

1.What is JavaScript?

JavaScript is a lightweight, interpreted programming language with object-oriented capabilities that allows you to build interactivity into otherwise static HTML pages.
The general-purpose core of the language has been embedded in Netscape, Internet Explorer, and other web browsers.

2.Name some of the JavaScript features.?

Following are the features of JavaScript −
JavaScript is a lightweight, interpreted programming language.
JavaScript is designed for creating network-centric applications.
JavaScript is complementary to and integrated with Java.
JavaScript is is omplementary to and integrated with HTML.
JavaScript is open and cross-platform.

3.What are the advantages of using JavaScript?

Following are the advantages of using JavaScript −
Less server interaction − You can validate user input before sending the page off to the server. This saves server traffic, which means less load on your server.
Immediate feedback to the visitors − They don't have to wait for a page reload to see if they have forgotten to enter something.
Increased interactivity − You can create interfaces that react when the user hovers over them with a mouse or activates them via the keyboard.
Richer interfaces − You can use JavaScript to include such items as drag-and-drop components and sliders to give a Rich Interface to your site visitors.

4.What are disadvantages of using JavaScript?

We can not treat JavaScript as a full fledged programming language. It lacks the following important features −
Client-side JavaScript does not allow the reading or writing of files. This has been kept for security reason.
JavaScript can not be used for Networking applications because there is no such support available.
JavaScript doesn't have any multithreading or multiprocess capabilities.

5.Is JavaScript a case-sensitive language?

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

6.How can you create an Object in JavaScript?

JavaScript supports Object concept very well. You can create an object using the object literal as follows −

var emp = {
name: "aarif",
age:13
};

7.How can you read properties of an Object in JavaScript?

You can write and read properties of an object using the dot notation as follows

// Getting object properties
emp.name // ==> aarif
emp.age // ==> 30
// Setting object properties
emp.name = "Naushaad"
emp.age = 28

8.How can you create an Array in JavaScript?

You can define arrays using the array literal as follows −

varx = [];
var y = [1,2, 3, 4, 5];

9.How to read elements of an array in JavaScript?

An array has a length property that is useful for iteration. We can read elements of an array as follows −

var x = [1,2, 3, 4, 5];
for (var i = 0; i < x.length; i++) { // Do something with x[i]
}

10.What is a named function in JavaScript?

How to define a named function?A named function has a name when it is defined. A named function can be defined using function keyword as follows −

function named(){ // do some stuff here}

11.How many types of functions JavaScript supports?

A function in JavaScript can be either named or anonymous.

12.How can you get the type of arguments passed to a function?

Using typeof operator, we can get the type of arguments passed to a function.
For example −

function func(x){
console.log(typeof x, arguments.length);
}
func(); //==> "undefined",
0func(1); //==> "number", 1
func("1", "2", "3"); //==> "string", 3

13.How can you get the total number of arguments passed to a function?

Using arguments.length property, we can get the total number of arguments passed to a function. For example −

function func(x){
console.log(typeof x, arguments.length);
}
func(); //==> "undefined", 0
func(1); //==> "number", 1
func("1", "2","3"); //==> "string", 3

14.How can you get the reference of a caller function inside a function?

The arguments object has a callee property, which refers to the function you're inside of. For example −

function func()
{
return arguments.callee ;
}
func(); // ==> func

15.What is the purpose of 'this' operator in JavaScript?

JavaScript famous keyword this always refers to the current context.

16.What are the valid scopes of a variable in JavaScript?

The scope of a variable is the region of your program in which it is defined.
JavaScript variable will have only two scopes.
Global Variables − A global variable has global scope which means it is visible everywhere in your JavaScript code.
Local Variables − A local variable will be visible only within a function where it is defined. Function parameters are always local to that function.

17.Which type of variable among global and local, takes precedence over other if names are same?

A local variable takes precedence over a global variable with the same name.

18.What is callback?

A callback is a plain JavaScript function passed to some method as an argument or option. Some callbacks are just events, called to give the user a chance to react when a certain state is triggered.

19.What is closure?

Closures are created whenever a variable that is defined outside the current scope is accessed from within some inner scope.

20.Give an example of closure?

Following example shows how the variable counter is visible within the create, increment, and print functions, but not outside of them −

function create()
{
var counter = 0;
return
{
increment: function()
{
counter++;
},
print: function() {
console.log(counter);
} }}
var c = create();
c.increment();
c.print(); // ==> 1

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