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. JavaScript is a
client-side as well as server side scripting language that can be inserted into
HTML pages and is understood by web browsers.
What are
the data types supported by JavaScript?
The data types supported
by JavaScript are:
- Undefined
- Null
- Boolean
- String
- Symbol
- Number
- Object
What
are the features of JavaScript?
Following 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.
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.
What
are the advantages of 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.
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 −
varemp = {
name: "Daniel",
age: 23
};
How
can you create an Array in JavaScript?
You
can define arrays using the array literal as follows-
var x = [];
var y = [1, 2, 3, 4, 5];
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.
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.
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‘.
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-
document.cookie = "key1 = value1; key2 =
value2; expires = date";
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:
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.
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.
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.
|
What is NaN in JavaScript?
NaN is
a short form of Not a
Number. Since NaN always compares unequal to any
number, including NaN, it is usually used to indicate an error condition for a
function that should return a valid number. When a string or something
else is being converted into a number and that cannot be done, then we get to
see NaN.
What is the DOM?
The
Document Object Model (DOM) is a programming interface for HTML and XML
documents. It represents the page so that programs can change the document structure,
style, and content. The DOM represents the document as nodes and objects.
API =
DOM + JavaScript
List out the various methods of
Document object.
- write(“string”): writes the given string on
the document.
- getElementById(): returns the element having
the given id value.
- getElementsByName(): returns all the elements
having the given name value.
- getElementsByTagName(): returns all the elements
having the given tag name.
- getElementsByClassName(): returns all the elements
having the given class name.
How
exceptions are handled in javascript?
By the help of
try/catch block, we can handle exceptions in JavaScript. JavaScript supports
try, catch, finally and throw keywords for exception handling.
What
are the javascript built-in objects?
JavaScript has several
built-in or core language objects. These built-in objects are available
regardless of window content and operate independently of whatever page your
browser has loaded.
Mention the methods of Date object.
- Date() -
Returns today's date and time
- getDate() -
Returns the day of the month for the specified date
- getDay() -
Returns the day of the week for the specified date
- getFullYear() -
Returns the year of the specified date
- getHours() -
Returns the hour in the specified date according to local time.
- getMilliseconds() -
Returns the milliseconds in the specified date according to local time.
What are regular expressions in javascript?
Regular expressions are patterns used to match character
combinations in strings. In JavaScript, regular expressions are also objects.
These patterns are used with the exec() and test() methods
of RegExp,
and with the match(), matchAll(), replace(), search(),
and split() methods
of String.
How is javascript used for validation?
JavaScript provides a way to validate form's data on the
client's computer before sending it to the web server. Form validation
generally performs two functions.
- Basic Validation − First of all, the form must be checked to make sure all
the mandatory fields are filled in. It would require just a loop through each
field in the form and check for data.
- Data Format Validation − Secondly, the data that is entered
must be checked for correct form and value. Your code must include appropriate
logic to test correctness of data.
What
is an event?
JavaScript's interaction with HTML is handled
through events that occur when the user or the browser manipulates a page. Events
are a part of the Document Object Model (DOM) Level 3 and every HTML element
contains a set of events which can trigger JavaScript Code.
What
is DHTML?
Dynamic
HTML, or DHTML, is a collection of technologies
used together to create interactive and animated websites by using a combination of a static markup
language (such as HTML), a client-side scripting language (such as JavaScript), a presentation definition language (such as CSS), and the Document Object Model (DOM).
What is JSON?
JSON is the abbreviation of JavaScript Object Notation. It is
one of the simplest data interchange format. It is also independent of
programming language and platform. Its lightweight text-based structure makes
it easily readable by a human. It is derived from JavaScript for presenting
simple data in the form of key-value pairs.
What is meant by JSON objects?
An object is defined as a set of key-value pairs. A JSON
starts with a left brace “{“ and ends with another right brace “}”. Every key
is followed by a colon “:” and the key-value pairs are separated from each
other by using a comma “,”. So, basically, JSON object is a collection of keys
along with their values arranged in a pre-specified JSON format.
What is the extension of the JSON file?
A JSON file has an extension of “.json”. Being in a
text-based format, a JSON file can be viewed or edited using any text editor
like notepad or notepad++.
What are the advantages and features of JSON?
- Easy
to use and fast nature. JSON syntax offers easy parsing of data and even
faster implementation. The light-weight structure of JSON allows it to
respond at a much faster rate.
- Compatible
with numerous operating systems and browsers. This allows JSON schema to
be attuned to many platforms without requiring any extra effort to make
sure its compatibility with another platform.
- Supports
a wide range of data types including integers, double, String, Boolean,
etc.
What are the limitations of JSON?
- As
the data gets complex with several nested or hierarchical structures, it
becomes complex for human readability.
- JSON
is not suitable for handling very complex large data.
- JSON
doesn’t have support for handling multimedia formats such as rich text or
images.
- It
doesn’t support comments.
What are the uses of JSON?
- JSON is mainly used for data interchange between
two systems.
- JSON
is prominently used for transmission of serialized data over a network
connection between two systems.
- APIs
and web services use JSON to format and transfer data.
- JSON
can be used in combination with most of the modern programming languages.
- JSON
can be used with JavaScript applications such as browser plugins and
websites.
- JSON
can be used to read data from the web server and display data on the web
pages.
Explain JSON syntax rules?
There are
several rules that describe the structure of the JSON. They are:
- Data
inside a JSON is arranged in Key value pair. The left side represents the
key and the data on the right side represents value. Both key and value
are separated by a colon “:”.
- Each
set of key-value pair is separated from the other pair by using a comma
“,”.
- Curly
braces define the JSON objects. Left curly brace “{“ represents the start
of the object and right curly brace “}” represents the end of an object.
- Arrays
are defined inside a JSON object by using square brackets “[ ]”.
What are the advantages of JSON over XML?
- JSON
is lighter and faster than the XML.
- JSON
has object types but XML doesn’t define objects as types. JSON has
different object type for a different set of data such as string, integer,
Boolean, array, etc. All XML objects are categorized as just one data
type, i.e. string.
- JSON
data can be easily accessed as a JSON object using JavaScript. On the
other hand, the XML data need to be parsed and allocated to the variables
using APIs. Getting value out of a JSON is as easy as reading an object
from your JavaScript programming.
Name the browsers that support JSON format?
Support for JSON is included in almost all the new versions
of the browsers. Internet Explorer, Chrome, Safari, Mozilla Firefox, etc. all
support JSON format.