Nate JavaScript Interview Questions Answers

Name the different types of pop up boxes in Javascript.

There are three types of pop up boxes in Javascript (i) alert() provides some information to the user with just an OK button (ii) confirm() asks a question to the user with two options Ok and cancel, and (iii) prompt() takes an input from the user.

What is the use of the ‘this’ keyword?

The keyword ‘this’ refers to the current instance of the object when used inside a function. But, when used outside a function, it refers to the window object.

Is Exception handling possible in Javascript?

With the latest version of Javascript, exception handling is possible; and this can be achieved using the following keywords try, catch and finally.

How is it possible to get the total number of arguments that are passed to a function?

The arguments.length property helps in getting the total number of arguments that are passed to a function.

What is the difference between typeof and instanceof operators in Javascript?

The typeof operator returns a string of what type the operand is. Whereas, the instanceof operator does not work with primitive data types; but works with objects and checks on what type the object is.

Nate JavaScript Most Frequently Asked Latest Interview Questions Answers

What are the controls of the Script Management group?

The controls of script Management group are:

ScriptManager
ScriptManagerProxy

 How many types of ready states in Ajax?

There are four ready states in Ajax:

Initialization
Request
Process
Ready

What is the difference between RegisterClientScriptBlock, RegisterClientScriptInclude and RegisterClientScriptResource?

Following are the functions:

RegisterClientScriptBlock – The script is specified as a string parameter.
RegisterClientScriptInclude – By setting the source attribute to a URL that point to a script file.
RegisterClientScriptResource – specifies Resource name in an assembly. The source attribute is automatically populated with a URL by a call to an HTTP handler that retrieves the named script from the assembly.

What are the decodeURI() and encodeURI()?

EncodeURl() is used to convert URL into their hex coding. And DecodeURI() is used to convert the encoded URL back to normal.

<script>

var uri="my test.asp?name=ståle&car=saab";

document.write(encodeURI(uri)+ "<br>");

document.write(decodeURI(uri));

</script>
Output –

my%20test.asp?name=st%C3%A5le&car=saab

my test.asp?name=ståle&car=saab

 Why it is not advised to use innerHTML in JavaScript?

innerHTML content is refreshed every time and thus is slower. There is no scope for validation in innerHTML and, therefore, it is easier to insert rouge code in the document and, thus, make the web page unstable.

What does the following statement declares?

var myArray = [[[]]];
It declares a three dimensional array.

How are JavaScript and ECMA Script related?

ECMAScript is nothing but another name for JavaScript. Precisely, ECMAScript is the formal name of JavaScript, when XML elements have to be accessed.

What is namespacing in JavaScript and how is it used?

Namespacing is used for grouping the desired functions, variables etc. under a unique name. It is a name that has been attached to the desired functions, objects and properties. This improves modularity in the coding and enables code reuse.

How can JavaScript codes be hidden from old browsers that don’t support JavaScript?

For hiding JavaScript codes from old browsers:

Add “<!–” without the quotes in the code just after the <script> tag.

Add “//–>” without the quotes in the code just before the <script> tag.

Old browsers will now treat this JavaScript code as a long HTML comment. While, a browser that supports JavaScript, will take the “<!–” and “//–>” as one-line comments.

What is a potential pitfall with using typeof bar === "object" to determine if bar is an object? How can this pitfall be avoided?

Although typeof bar === "object" is a reliable way of checking if bar is an object, the surprising gotcha in JavaScript is that null is also considered an object!

Therefore, the following code will, to the surprise of most developers, log true (not false) to the console:

var bar = null;
console.log(typeof bar === "object");  // logs true!
As long as one is aware of this, the problem can easily be avoided by also checking if bar is null:

console.log((bar !== null) && (typeof bar === "object"));  // logs false
To be entirely thorough in our answer, there are two other things worth noting:

First, the above solution will return false if bar is a function. In most cases, this is the desired behavior, but in situations where you want to also return true for functions, you could amend the above solution to be:

console.log((bar !== null) && ((typeof bar === "object") || (typeof bar === "function")));
Second, the above solution will return true if bar is an array (e.g., if var bar = [];). In most cases, this is the desired behavior, since arrays are indeed objects, but in situations where you want to also false for arrays, you could amend the above solution to be:

console.log((bar !== null) && (typeof bar === "object") && (toString.call(bar) !== "[object Array]"));
However, there’s one other alternative that returns false for nulls, arrays, and functions, but true for objects:

console.log((bar !== null) && (bar.constructor === Object));
Or, if you’re using jQuery:

console.log((bar !== null) && (typeof bar === "object") && (! $.isArray(bar)));
ES5 makes the array case quite simple, including its own null check:

console.log(Array.isArray(bar));

What will the code below output to the console and why?

(function(){
  var a = b = 3;
})();

console.log("a defined? " + (typeof a !== 'undefined'));
console.log("b defined? " + (typeof b !== 'undefined'));

Since both a and b are defined within the enclosing scope of the function, and since the line they are on begins with the var keyword, most JavaScript developers would expect typeof a and typeof b to both be undefined in the above example.

However, that is not the case. The issue here is that most developers incorrectly understand the statement var a = b = 3; to be shorthand for:

var b = 3;
var a = b;
But in fact, var a = b = 3; is actually shorthand for:

b = 3;
var a = b;
As a result (if you are not using strict mode), the output of the code snippet would be:

a defined? false
b defined? true

But how can b be defined outside of the scope of the enclosing function? Well, since the statement var a = b = 3; is shorthand for the statements b = 3; and var a = b;, b ends up being a global variable (since it is not preceded by the var keyword) and is therefore still in scope even outside of the enclosing function.

Note that, in strict mode (i.e., with use strict), the statement var a = b = 3; will generate a runtime error of ReferenceError: b is not defined, thereby avoiding any headfakes/bugs that might othewise result. (Yet another prime example of why you should use use strict as a matter of course in your code!)

What is the script build up by jQuery?

jQuery is a Javascript file and it is single javascript file that contains common DOM, event effects and Ajax functions.

How can we debug jQuery?

There are two ways to debug jQuery:

Debugger keyword

Add the debugger to the line from where we have to start debugging and then run Visual Studio in Debug mode with F5 function key.
Insert a break point after attaching the process

What are all the ways to include jQuery in a page?

Following are the ways to include jQuery in a page:

Local copy inside script tag
Remote copy of jQuery.com
Remote copy of Ajax API
Local copy of script manager control
Embedded script using client script object