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GRADE 9
Computer Science 3
Introduction to Javascript
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In JavaScript, to declare a new variable, we can use the keywords:
var
,
let
, and
const
Variable
names
are used to
identify
and
store
data in JavaScript
There are different data types in JavaScript that include primitive data
types
JavaScript is a
front-end
scripting
language
developed by
Netscape
for
dynamic
content
JavaScript is
lightweight
, but with
limited
capabilities
JavaScript can be used as an
object-oriented
language
JavaScript is a
client-side
technology
JavaScript is embedded in your
HTML
page and
interpreted
by the
Web browser
Client-side
JavaScript is the language's most
common
format
Client-side
JavaScript implies that
HTML
can incorporate
client-interacting programs
,
control the browser
, and
make the content of the HTML powerful
JavaScript was initially named "
LiveScript
" and later changed to "JavaScript" to position it as the "
younger brother
" of Java
JavaScript was
submitted
for
standardization
to the
ECMA world organization
The
standardized language
is known as
ECMAScript
JavaScript is supported by
major browsers like Firefox
,
Chrome
,
Internet
Explorer,
Safari
, and
Opera
Advantages
of JavaScript
:
Less contact with the server
allows for validating user feedback before sending the page to the server
Immediate feedback
to visitors without the need for
page reloads
Expanded
interactivity
for creating
responsive web page interfaces
Greater interfacing capabilities
for
richer GUI
on
web pages
Limitations
of JavaScript:
JavaScript cannot
read
or
write
files
JavaScript lacks support for
organizing applications
JavaScript runs in a
single execution
thread
How to use JavaScript in your
web page
:
JavaScript codes run from inside a
web page
using the
<script
> element
Scripts
can be embedded or placed in an
external file
and connected to a page like CSS
External
<
script
> elements use the
src
attribute to point to a script file with a
.js
suffix
Benefits of using
external style sheets
for JavaScript:
Allows the
application
of the same
script
to different
websites
Each external script requires an additional server
HTTP request
, which can slow down performance
Variables
in JavaScript are also known as
holders
or
containers
Variables allow you to position data
and refer to the data by naming the
container
Variables
can be known as something that may change
In JavaScript,
variables
can hold various
data values
To declare a new variable in JavaScript, keywords
var
,
let
, and
const
are used
Using
var
keyword
var
keyword is used to
create
and
declare
a variable
Variables
can be declared without initializing or initialized with a number using
var
Using
let
let
variables
are declared similarly to
var
but impose
scope constraints
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