22519 Client Side Scripting Language External Oral / Viva Practice Questions with Answers
Q1. What is the
difference between Java & JavaScript?
Java |
JavaScript |
Java is an OOP programming language. |
JavaScript is an OOP scripting language. |
It creates applications that run in a virtual machine or browser. |
The code is run on a browser only. |
Java code needs to be compiled. |
JavaScript code are all in the form of text. |
Q2. 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.
Q3. What are the
data types supported by JavaScript?
The data types supported
by JavaScript are:
- Undefined
- Null
- Boolean
- String
- Symbol
- Number
- Object
Q4. What are the
features of JavaScript?
- It is a lightweight, interpreted programming
language.
- It is designed for creating network-centric applications.
- It is complementary to and integrated with
Java.
- It is an open and cross-platform scripting
language.
Q5. 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.
Q6. What are
the advantages of 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.
Q7. 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 −
1 2 3 4 |
var
emp = { name:
"Daniel", age:
23 }; |
Q8. How can you
create an Array in JavaScript?
You can define arrays using the array
literal as follows-
1 2 |
var
x = []; var
y = [1, 2, 3, 4, 5]; |
Q9. What is a
name function in JavaScript & how to define it?
A named function declares a name as
soon as it is defined. It can be defined using function keyword
as :
1 2 3 |
function
named(){ //
write code here } |
Q10. Can you
assign an anonymous function to a variable and pass it as an argument to
another function?
Yes! An anonymous
function can be assigned to a variable. It can also be passed as an argument to
another function.
In case you are facing any challenges
with these JavaScript Interview Questions, please comment on your problems in
the section below.
Q11. What is
argument objects in JavaScript & how to get the type of arguments passed to
a function?
JavaScript variable
arguments represents the arguments that are passed to a
function. Using typeof operator, we can get the type of
arguments passed to a function. For example −
1 2 3 4 5 6 |
function
func(x){ console.log(typeof
x, arguments.length); } func();
//==> "undefined", 0 func(7);
//==> "number", 1 func("1",
"2", "3"); //==> "string", 3 |
Q12. What are
the 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.
Q13. What is
the purpose of ‘This’ operator in JavaScript?
The
JavaScript this keyword refers to the object it belongs to.
This has different values depending on where it is used. In a method, this
refers to the owner object and in a function, this refers to the global object.
Q14. What is
Callback?
A callback is
a plain JavaScript function passed to some method as an argument or option.
It is a function that is to be executed after another
function has finished executing, hence the name ‘call back‘.
In JavaScript, functions are objects. Because of this, functions can take
functions as arguments, and can be returned by other functions.
Q16. Name some of
the built-in methods and the values returned by them.
Built-in Method |
Values |
CharAt() |
It returns the character at the specified index. |
Concat() |
It joins two or more strings. |
forEach() |
It calls a function for each element in the array. |
indexOf() |
It returns the index within the calling String object of the first
occurrence of the specified value. |
length() |
It returns the length of the string. |
pop() |
It removes the last element from an array and returns that element. |
push() |
It adds one or more elements to the end of an array and returns the
new length of the array. |
reverse() |
It reverses the order of the elements of an array. |
In case you are facing any challenges
with these JavaScript Interview Questions, please comment on your problems in
the section below.
Q17. What are
the variable naming conventions in JavaScript?
The following rules are
to be followed while naming variables in JavaScript:
- You
should not use any of the JavaScript reserved keyword as
variable name. For example, break or boolean variable names are not valid.
- JavaScript
variable names should not start with a numeral (0-9).
They must begin with a letter or the underscore character. For example,
123name is an invalid variable name but _123name or name123 is a valid
one.
- JavaScript
variable names are case sensitive. For example, Test and test
are two different variables.
Q18. How does
TypeOf Operator work?
The typeof operator
is used to get the data type of its operand. The operand can be either a literal or
a data structure such as a variable, a function, or an
object. It is a unary operator that is placed before its
single operand, which can be of any type. Its value is a string indicating the
data type of the operand.
Q19. How to
create a cookie using JavaScript?
The simplest way to
create a cookie is to assign a string value to the document.cookie object,
which looks like this-
Syntax :
1 |
document.cookie
= "key1 = value1; key2 = value2; expires = date"; |
Q20. How to
read a cookie using JavaScript?
Reading a cookie is
just as simple as writing one, because the value of the document.cookie object
is the cookie. So you can use this string whenever you want to access the
cookie.
- The document.cookie string
will keep a list of name = value pairs separated by semicolons, where name
is the name of a cookie and value is its string value.
- You
can use strings’ split() function to break the string
into key and values.
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Q21. How to
delete a cookie using JavaScript?
If you want to
delete a cookie so that subsequent attempts to read the cookie in JavaScript return nothing, you
just need to set the expiration date to a time in the past. You should define
the cookie path to ensure that you delete the right cookie. Some browsers will
not let you delete a cookie if you don’t specify the path.
Now let’s move on to the next section
of JavaScript interview questions.
Q22. What is
the difference between Attributes and Property?
Attributes- provide more details on
an element like id, type, value etc.
Property- is the value assigned to
the property like type=”text”, value=’Name’ etc.
Q23. List out
the different ways an HTML element can be accessed in a JavaScript code.
Here are the list
of ways an HTML element can be accessed in a Javascript code:
(i) getElementById(‘idname’): Gets an element by its ID name
(ii) getElementsByClass(‘classname’): Gets all the elements
that have the given classname.
(iii) getElementsByTagName(‘tagname’): Gets all the elements
that have the given tag name.
(iv) querySelector(): This function takes css style selector
and returns the first selected element.
Q24. In how
many ways a JavaScript code can be involved in an HTML file?
There are 3 different ways in which a
JavaScript code can be involved in an HTML file:
- Inline
- Internal
- External
An inline function
is a JavaScript function, which is assigned to a variable created at runtime.
You can differentiate between Inline Functions and Anonymous since an inline
function is assigned to a variable and can be easily reused. When you need a
JavaScript for a function, you can either have the script integrated in
the page you are working on, or you can have it placed in a separate file
that you call, when needed. This is the difference between an internal script
and an external script.
Q25. What are
the ways to define a variable in JavaScript?
The three possible
ways of defining a variable in JavaScript are:
- Var – The JavaScript variables
statement is used to declare a variable and, optionally, we can initialize
the value of that variable. Example: var a =10; Variable declarations are
processed before the execution of the code.
- Const – The idea of const functions is
not allow them to modify the object on which they are called. When a
function is declared as const, it can be called on any type of object.
- Let – It is a signal that the variable may
be reassigned, such as a counter in a loop, or a value swap in an
algorithm. It also signals that the variable will be used only in the
block it’s defined in.
Q26. What is a
Typed language?
Typed Language is
in which the values are associated with values and not
with variables. It is of two types:
- Dynamically: in this, the variable can hold multiple
types; like in JS a variable can take number, chars.
- Statically: in this, the variable can hold only one
type, like in Java a variable declared of string can take only set of
characters and nothing else.
Q27. What is
the difference between Local storage & Session storage?
Local Storage – The data is not sent
back to the server for every HTTP request (HTML, images, JavaScript, CSS, etc)
– reducing the amount of traffic between client and server. It will stay
until it is manually cleared through settings or program.
Session Storage – It is similar to local
storage; the only difference is while data stored in local storage has no
expiration time, data stored in session storage gets cleared when the page
session ends. Session Storage will leave when the browser is closed.
In case you are facing any challenges
with these JavaScript Interview Questions, please comment on your problems in
the section below.
Q28. What is
the difference between the operators ‘==‘ & ‘===‘?
The main difference
between “==” and “===” operator is that formerly compares variable by
making type correction e.g. if you compare a number with a
string with numeric literal, == allows that, but === doesn’t allow that,
because it not only checks the value but also type of two variable, if two
variables are not of the same type “===” return false, while “==” return true.
Q29. What is
the difference between null & undefined?
Undefined means a
variable has been declared but has not yet been assigned a
value. On the other hand, null is an assignment value. It can be assigned to a
variable as a representation of no value. Also, undefined and null are two
distinct types: undefined is a type itself (undefined) while null is an object.
Q30. What is
the difference between undeclared & undefined?
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.
Q31. Name some
of the JavaScript Frameworks
A JavaScript framework is an application
framework written in JavaScript. It differs from a JavaScript library in its
control flow. There are many JavaScript Frameworks available but some of the
most commonly used frameworks are:
Q32. What is
the difference between window & document in JavaScript?
Window |
Document |
JavaScript window is a global object which holds variables, functions,
history, location. |
The document also comes under the window and can be considered as the
property of the window. |
Q33. What is
the difference between innerHTML & innerText?
innerHTML – It will process an HTML
tag if found in a string
innerText – It will not process an
HTML tag if found in a string
Q34. What is
an event bubbling in JavaScript?
Event bubbling is a
way of event propagation in the HTML DOM API, when an event
occurs in an element inside another element, and both elements have registered
a handle for that event. With bubbling, the event is first captured and handled
by the innermost element and then propagated to outer
elements. The execution starts from that event and goes to its parent element.
Then the execution passes to its parent element and so on till the body
element.
Q36. How do
JavaScript primitive/object types passed in functions?
One of the
differences between the two is that Primitive Data Types are passed By Value
and Objects are passed By Reference.
- By
Value means
creating a COPY of the original. Picture it like twins: they are born
exactly the same, but the first twin doesn’t lose a leg when the second
twin loses his in the war.
- By
Reference means creating an ALIAS to the original. When your Mom
calls you “Pumpkin Pie” although your name is Margaret, this doesn’t
suddenly give birth to a clone of yourself: you are still one, but you can
be called by these two very different names.
Q37. How can
you convert the string of any base to integer in JavaScript?
The parseInt() function
is used to convert numbers between different bases. It takes the string to be
converted as its first parameter, and the second parameter is the base of the
given string.
For example-
1 |
parseInt("4F",
16) |
Q38. What
would be the result of 2+5+”3″?
Since 2 and 5 are
integers, they will be added numerically. And since 3 is a string, its
concatenation will be done. So the result would be 73. The ” ” makes all the
difference here and represents 3 as a string and not a number.
Q39. What are
Exports & Imports?
Imports and exports help us to write
modular JavaScript code. Using Imports and exports we can split our code into
multiple files. For example-
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Q40. What is
the ‘Strict’ mode in JavaScript and how can it be enabled?
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.
Q41. What is a
prompt box in JavaScript?
A prompt box is a
box which allows the user to enter input by providing a text box. The
prompt() method displays a dialog 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.
Q43. What is
the difference between Call & Apply?
The call() method
calls a function with a given this value and arguments provided individually.
Syntax-
1 |
fun.call(thisArg[,
arg1[, arg2[, ...]]]) |
The apply() method
calls a function with a given this value, and arguments provided as an array.
Syntax-
1 |
fun.apply(thisArg,
[argsArray]) |
Q44. How to
empty an Array in JavaScript?
There are a number of methods you can
use to empty an array:
Method 1 –
1 |
arrayList
= [] |
Above code will set the variable
arrayList to a new empty array. This is recommended if you don’t have
references to the original array arrayList anywhere else, because it will
actually create a new, empty array. You should be careful with this method of
emptying the array, because if you have referenced this array from another
variable, then the original reference array will remain unchanged.
Method 2 –
1 |
arrayList.length
= 0; |
The code above will clear the
existing array by setting its length to 0. This way of emptying the array also
updates all the reference variables that point to the original array.
Therefore, this method is useful when you want to update all reference variables
pointing to arrayList.
Method 3 –
1 |
arrayList.splice(0,
arrayList.length); |
The implementation above will also
work perfectly. This way of emptying the array will also update all the
references to the original array.
Method 4 –
1 2 3 4 |
while(arrayList.length) { arrayList.pop(); } |
The implementation above can also
empty arrays, but it is usually not recommended to use this method often.
Q50. What are
escape characters in JavaScript?
JavaScript escape characters enable you
to write special characters without breaking your application. 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.
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