TechnicalcodewithAJ

example:datatypes.js

var prodid=1000;

var prodname="samsung";

var prodprice=50000;

var available=true;

console.log(prodid,prodname,prodprice,available);

price="dell";

console.log(price);

price=50000----->number------>//accepted

price="dell"------>string---->//accepted

In Javascript, the datatype is not fixed to one type, based on the value the datatype will be changing which is very dangerous in programming.

In other languages it will through an error where as in javascript will accept the value whatever you give it.

Javascript does not provide typesafety.

Differences between var and let keywords:

1.var is introduced with es1

let is introduced with es6[or es2015]

2.var is function scoped

let is block scoped

block can be declared in 2 ways:

i.for loop block

for(intialization;declaration;increment/decrement)

{

...

}

ii.normal block

{

...

}

for(var i=1;i<=5;i++)

{

console.log(i);

}

console.log("after for loop i:"+i);

for(let j=1;j<=5;j++)

{

console.log(j);

}

console.log("after for loop j:"+j);

note:

1.In function scope variable declared using var keyword,the value is available

after the for loop.The value of the variable exist after the loop.

2.In block scope variable declared using let keyword, the value of the variable in not defined after the loop.The value of the variable exists within the loop.

Javascript:

*Javascript improves the user experience of the web page by converting static

page into interactive page.

*Javascript add behavior to the web page.

HTML/HTML5

*HTML stands for hyper text markup language.

*HTML is the standard language for creating web pages.

*HTML describes the structure of a web page.

Ex:skeleton is like html

CSS is like Skin which will beautfy the web page.

brain is like Javascript because it will implements the logic.

CSS/CSS3

*css stands for cascading style sheet.

*css describes how html elements displayed on the screen,with css

we can control the font,size and color of the text.

*What is Java Script?

Java Script is one of the most popular and widely used programming language.

It is growing faster than any other programming language.

big companies like netflix,paypal and walmart build their entire application using javascript.

The average salary of javascript developer 72000$ to 75000$

It is great oppurtunity to learn js because you can work as front end developer,back end developer.

full stack developer:full stack developer means who knows both front end and back end.

*What can we do with js?

for a longer period of time js was only used in browsers to build interactive web pages.

some developers use to prefer js as toy language.

huge community support and investment is provided to js by large companies like facebook and google.

javascript can be used to develop

1)web/mobile apps

2)real time networking apps

3)command line tools

4)Games

Why Study JavaScript?

JavaScript is one of the 3 languages all web developers must learn:

1. HTML to define the content of web pages

2. CSS to specify the layout of web pages

3. JavaScript to program the behavior of web pages

The Original JavaScript ES1 ES2 ES3 (1997-1999)

The First Main Revision ES5 (2009)

The Second Revision ES6 (2015)

The Yearly Additions (2016, 2017, 2018).

javascript is a text-based programming language used on both client side and server side

that allows user to make web page interactive.

Naming variables:

*The first character should be a letter or an (_)underscore or an $,but we can't use the

number.

goto google

type as node js

download it

goto to terminal in vs code.

view---->terminal

node -v

Example:

let $myVariable="Hello world";

console.log($myVariable);

let myName="Asha";

console.log(myName);

console.log(typeof(myName));

let myAge=5;

console.log(myAge);

console.log(typeof(myAge));

Introduction to Typescript:

1.typescript is a typed superset of javascript that transpiles (or) compiles into

plain javascript.

2.typed means typescript provides type safety by allowing datatypes usage expliciltly

[variable declared with one type cannot be assigned with another

type data]

example:

let prodid:number; //here the prodid is number

prodid=1; //accepted

...

prodid="samsung"; //here the prodid is string

//not accepted -->type safety

3.superset means typescript is extending javascript by supporting datatypes expliciltly,access specifiers,interface

support,..

typescript=javascript+ datatypes,accessspecfiers,interface,..

4.typescript is provided by microsoft in the year 2012 with

version typescript0.8

[google used typescript1.8 version to develop angular2]

5.typescript latest version is typescript4.2

6.typescript provides programming feel of c# and java

7.typescript file extension is ts

8.typescript compiler is tsc.exe

9.typescript is not executable[not understandable to browser],

it need to be converted into plain javascript using

compiler[tsc.exe]

<>.ts -----> tsc.exe ----> <>.js -------->executable[browser]

[compiler]

| |

high level middle level

languages langauges

developer

friendly

10.typescript is developer friendly over javascript

installing typescript compiler:

-------------------------------

1.typescript compiler is available as a node package

2.node package can be installed using "npm" tool,this tool

comes with nodejs installation

browser

https://nodejs.org

...

click on 14.16.0 button

it will download setup.exe,run setup file to install

nodejs,this will provide npm tool

syntax:

npm install[i] <packagename> [-g]

3.goto command window

>npm i typescript -g ------------------>website

internet

<-----------------

downloading

typescript compiler

it will install typescript compiler globally,tsc.exe will be

available through out system

>tsc -v

it will display version

Difference between let and var keyword || part 2

Var will break block scoped principle,this leads to global polluting problem

[or memory leakage]

Let will not break block scoped principle

//function scope variables

var a=1000;

let b=2000;

{

//block scoped variables

var c=3000;

let d=4000;

}

console.log(a);

console.log(b);

console.log(c);

console.log(d);

if we declare any variable within the block the life and scope of variable exist within the block.

note:

variable declared inside the block is available outside the block is called “global polluting problem” or “memory leakage”.

Var allows variable redeclaration.

Let doesn’t allow variable redeclaration.

var a=100;

console.log(a);

var a=300;

console.log(a);

let a=100;

console.log(a);

let a=300;

console.log(a);

Var will has variable hoisting problem.

Let will not have variable hoisting problem.

Varlet3.js

Console.log(a); //undefined

Var a=100;--------allowed ----variable hoisting

Console.log(a);

Let a=100;---- not allowed----no variable hoisting

Conclusion:

From es6 it is recommended to go with let.

Let is introduced with es6.

Const is same as let, it is block scoped with fixed value.

Assemblies:

*Assemblies have an extension of .dll or .exe depending on the type of application.

*.Net Assemblies contain Managed code.

*.Non .net Assemblies contain unManaged code.

*Console,Windows applications will have .exe extension after compilation.

*Web application will have .dll extension after compilation.

*.exe or .dll are the intermediate language assembly generated by the respective compilers after program execution.

*When we compile non .net program it will generate the assembly which is it native format it is also known as unManaged code or Machine code which is understandable by the operating system.

*.Net assemblies contain IL or MSIL whereas non .Net assemblies contain Native code or Machine code.

*.Net application execution is performed in two steps:

1. Compilation

2. Execution

*Compilation:from source code to IL or MSIL

*Execution:IL to platform specific machine code or native code.

CLR:Common language runtime environment provides several benefits like:

i. Garbage collection.

ii. Performance improvement.

iii. Interoperability.

iv. Exception Handling.

v. Custom Attributes and many more..

*.Net support many programming language like C#,VB,J# and C++.

*C#,VB,J# can generate only Managed code.

*C++ can generate both Managed and unManaged code.

*The Native code is not stored anywhere in the System, After we close the program the native code is destroyed.

*When we execute the program again the native code gets genterated again.

Program:

using System;

namespace Introtocsharp

{

class Program

{

static void Main()

{

Console.WriteLine("welcome to .net tutorial");

}

INTRODUCTION TO C#

C# is a modern, general-purpose, object-oriented programming language developed

by Microsoft and approved by European Computer Manufacturers Association (ECMA)

and International Standards Organization (ISO).

C# was developed by Anders Hejlsberg and his team during the development of .Net

Framework.

C# is designed for Common Language Infrastructure (CLI), which consists of the

executable code and runtime environment that allows use of various high-level

languages on different computer platforms and architectures.

The following reasons make C# a widely used professional language:

*It is a modern, general-purpose programming language

*It is object oriented.

*It is component oriented.

*It is easy to learn.

*It produces efficient programs.

*It can be compiled on a variety of computer platforms.

*It is a part of .Net Framework.

C# vs .Net

*C# is a progragramming language.

*.Net is a framework for building application on windows.

*.Net framework is not limited to c# programming language,we can build application using different programming languages like J#,vb.net,F# in .Net Framework.

*What is namespace?

Namespace is a collection of classes,interfaces,structures,enums and delegates.

Namespace is used to organize the code.

Namespace can contain other Namespaces.

*Main() method is the entry point into your application.

*What is a class?

Class is a container contains Data & Methods.

Data is also known as Attributes

Method is also known as Functions.

*Functions or Methods have behavior they execute the code.

*Data represents the State of the Application

HTML Headings

HTML headings are defined with the <h1> to <h6> tags.

<h1> defines the most important heading. <h6> defines the least important heading:

<!DOCTYPE html>

<html>

<body>

<h1>This is heading 1</h1>

<h2>This is heading 2</h2>

<h3>This is heading 3</h3>

<h4>This is heading 4</h4>

<h5>This is heading 5</h5>

<h6>This is heading 6</h6>

</body>

</html>