Coder Baba

Dev., [3/16/2021 9:45 AM]
JavaScript Engine
JavaScript engine in the browser interprets, compiles and executes JavaScript code which is in a web page. It does memory management, JIT compilation, type system etc

Dev., [3/16/2021 9:45 AM]
Advantages of JavaScript
• JavaScript is easy to learn.
• It executes on client's browser, so eliminates server side processing.
• It executes on any OS.
• JavaScript can be used with any type of web page e.g. PHP, ASP.NET, Perl etc.
• Performance of web page increases due to client side execution.
• JavaScript code can be minified to decrease loading time from server.

Dev., [3/16/2021 9:46 AM]
JavaScript Variable

A JavaScript variable is simply a name of storage location. Variable means anything that can vary. variables hold the data value and it can be changed anytime.
JavaScript uses reserved keyword var to declare a variable. A variable must have a unique name. You can assign a value to a variable using equal to (=) operator when you declare it or before using it.
var one = 1; // variable stores numeric value

var two = 'two'; // variable stores string value

var three; // declared a variable without assigning a value

Declare Variables:
var one ;
var two ;

Variable Declaration and Initialization :
Var Number= 'two';
Var age= 20 ;
Var name;
Name= ” Rahul ”;

Or
Var Name =” Rakesh”;

Dev., [3/16/2021 9:46 AM]
JavaScript Identifiers:
All JavaScript variables must be identified with unique names.
These unique names are called identifiers.
dentifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume).
1. Name must start with a letter (a to z or A to Z), underscore( _ ), or dollar( $ ) sign.
2. After first letter we can use digits (0 to 9), for example value1.
3. JavaScript variables are case sensitive, for example x and X are different variables.
4. Names are case sensitive (y and Y are different variables)
5. Reserved words (like JavaScript keywords) cannot be used as names
Example:
Correct JavaScript variables
1. var x = 10;
2. var _value="sonoo";

Incorrect JavaScript variables
1. var 123=30;
2. var *aa=320;

Dev., [3/16/2021 9:46 AM]
JavaScript local variable
A JavaScript local variable is declared inside block or function. It is accessible within the function or block only. For example:
<script>
function abc(){
var x=10;//local variable
}

</script>

Or

<script>
If(10<13){
var y=20;//JavaScript local variable
}
</script>

JavaScript global variable
A JavaScript global variable is declared outside the function or declared with window object. It can be accessed from any function.
example:
<script>
var data=200;//gloabal variable
function a(){
document.writeln(data);
}
function b(){
document.writeln(data);
}
a();//calling JavaScript function
b();
</script>

Javascript Data Types

Data type indicates characteristics of data. It tells the compiler whether the data value is numeric, alphabetic, date etc., so that it can perform the appropriate operation.

There are two types of data types in JavaScript.
1. Primitive data type
2. Non-primitive (reference) data type
What are Primitive Data Types in JavaScript?:
These are the predefined or built in types of data that are supported by the programming language by default. JavaScript mainly supports the following types of primitive data types.

• Boolean: logical entity having values as true or false.
• Numbers: Represents numeric values and can store integers and decimals.
• Strings: Represent a sequence of characters such as “Hello World.” Strings can store in single quotes or double-quotes.
• Undefined: A variable that has an unassigned value will have an undefined default value.
a variable without a value, has the value undefined. The type is also undefined
• Null: In JavaScript, null means”nothing.” It is something that doesn’t exist.

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