Java
script is a client side scripting language and it is standardize by
ECMA. Its code is written between opening <script> and closing
</script> tags. By using JavaScript we can create dynamic web
page. JavaScript is embedded within HTML.
<script>
tag has "type" attribute you must need to add in scripts
tag like.
<script
type="text/javascript">
There
are three ways to write JavaScript code in your web page.
- embedded
- external
- inline
In
external way: there is src attribute like <script
type="text/javascript" src="script.js(filepath)">
while in embedded we write JavaScript inside the html page enclosed
in <script></script> tags.
Note:
never use inline because you write this in html elements so very
difficult to manage.
What
are Client Side Languages?
Client
side scripting languages are executed on any client machine instead
of server so it doesn't take time to execute.
What
are Server Side Languages?
Server-side
scripting is used in web development which involves scripts on a web
server which produces a response customized for each client's request
to the website.
Variable
- variable
stores the value.
- variable
have some to define.
1.
variable name can be letter, number, any symbols.
var
= x; var = 'bhumi'
2.
variable name can't start with numbers it must start with letter.
3.
variable name is case sensitive. Var and var both are different name
in
JavaScript.
var
= X; var = x; (both are different)
4.
reserved keywords can't be given as variable name.
like
function, switch, return etc.
5.
logical operator[=, +, -, /] cannot use in variable name.
var
= bh+bh;
6.
blank space is not allowed within variable name.
var
= 1 23;
Datatypes
The
latest ECMAScript standard defines seven data types:
There
are six primitive types of datatype.
1.
Boolean
it
has two values true and false.
2.
null
it
has one value null.
var
a = null;
alert(a);//null
alert(a+'bhumi');//nullbhumi
(concatenation)
3.
undefined
variable
has not assigned any value its undefined.
var
a;
alert(a);//undefined
alert(a+'bhumi');//undefinedbhumi
(concatenation)
4.
number
variable
has assigned by any number.
var
a = 2;
5.
String
variable
has assigned by any latter.
var
a = 'bhumi';
6.
Symbol
(new
in ECMAScript 6). A data type whose instances are unique and
immutable.
Popups in JavaScript
There
are three types of pop ups.
1.
alert()
it
is used for pop up alert message has one button is 'ok'.
alert('welcome
to my website');//message
2.
confirm()
it
is used for conformation it has two button 'ok' and 'cancel'
confirm('Are
you 18+');//ok and concel (Boolean = 0/1 or false/true)
3.
prompt()
it
is used to get vales from user.
prompt(
'Enter your age plz');
Function in JavaScript
A
JavaScript function is a block of code designed to perform a
particular task. A JavaScript function is executed when it call.
Syntax:
function function name(para1, para2)
{
return();
}
Example:
<button
onclick="main()">Click me</button>
function
main(){
alert('hey');
}
Benefits
of Function
You
can reuse code: Define the code once, and use it many times.
You
can use the same code many times with different arguments, to
produce different results.
function
main(greet){
alert(greet);
}
main('namaste');
main('hi');
main('hello');
nested
function:
function
contains other function call nested function. Such functions are very
useful for abstraction and encapsulation.
var
name = 'Bhumi';
function
main(){
//local;
nested();
}
main();
function
nested(){
alert(name);
}
nested();
Two
types of scope in function.
1.
local variable
local
variable can be use within the function. you cant use it out side the
function.
2.
global variable:
global
variable can use anywhere in the code.
Conditionals
in JavaScript
if...else:
->
Use if to specify a block of code to be executed, if a
specified condition is true
->
Use else to specify a block of code to be executed, if the same
condition is false
->
Use else if to specify a new condition to test, if the first
condition is false
switch
:
it
has many alternative code to execute.
switch(condition){
case
..
break;
}
ternary:
it
has two values true and false
var
getName = 45;
var
result = (getName == 45)?'yes it is':'no it is not';
alert(result);
Loops
are set of code which is used to repeat the condition of loop block.
Loops returns the true or false values depend on the condition.
You
can counter the loops by increments and decrements.
For
Loop:
syntax:
for
(statement 1; statement 2; statement 3) {
code
block to be executed
}
for
(var i = 0; i < 10; i++) {
console.log(i);//0,1,2,3,4,5,6,7,8,9
};
For
in loop
When
variable does not stored in array or variable have key pvalue pair
then you can use for in loop.
Syntax:
for
(var in object) {
code
block to be executed
}
var
myArr = {
name
: 'Bhumi',
sname
: 'Golakia',
age
: 22
}
alert(
myArr['name'] ); //Bhumi
for(
var i in myArr ){
console.log("At
key "+i+" got "+myArr[i]+" value.");
}
while
loop:
This
loop control the flow of code depend on condition. this loop checks
the condition first and then it will do increments or decrements
syntax
:
while
(condition) {
code
block to be executed
}
while
( i < 10 ) {
console.log(i);
//0,1,2,3,4,5,6,7,8,9
i++;
};
Do
while loops:
This
loop first do the increment or decrements and the it checks the
condition. Control flow statement that executes a block of code at
least once.
syntax:
do
{
code
block to be executed
}
while
(condition);
do
{
console.log("before:
"+i);//0,1,2,3,4,5,6,7,8,9
i++;
}
while
( i < 10 );
