TypeScript.txt

TypeScript:

To install TS, you need to install npm first(nodejs) 
check version of npm by "npm -v"
install command:  npm install -g typescript
check the version: "tsc -v"

---->every browser will have one engine to run/interpret js
eg:google chrome-->v8,firefox--->spiderMonkey

-->any browser cannot understand ts. so u need a compiler which converts ts into js.The compiler is typescript compiler , also called as "tsc"
In VS code, always try to prefer command prompt
compile command: 1. npx tsc --init   , it will create tsconfig.json which sets rules while converting ts into js
2. npx tsc filename/. which will create js file


Typescript data types:
Typescript follows two methods for data type declarations
1. Type Annotations: it means we declare data type followed by : , after the variable
2.Type Interference: it means typescript can guess the data type based on initial value

Data types:
number,string,boolean,undefined,null,void,tuple,any,
enum: enum is a data type given to constant value(a set of constants)
never: never is data type which defines the situation/function that never should run
union( | )==> used to define multiple data types 
any means it is allowed to take any data type

Task1: create a variable "name" which accepts number or string and create a variable value which accepts any data type and print their types in console

let s:number|string="raju";
let w:any=321;
console.log(typeof s)
console.log(typeof w)

Task2: create an array which accepts strings and numbers only

Tuple: tuple is used when we need to declare data types for individual array elements;
let arr:[number|string,any]=["",true];

Function: every function need to define it parameters and return type

void is used to defined a function return type when the function is not returning anything

In function parameters you can give optional parameters  by using '?' and you can even define default value using parameter=value

We represents objects in two ways
1. Interfaces
interface is user defined data type specifically for objects

interface myObj{
    name:string,
    age:number
}

2.type alias
type x=number|string|boolean;
let a:x="ghj"

//access modifiers
it means how access will be given to the following elements
Public - it can accessed by any class,Private - it cannot be accessed by any class except its own,Protected - it can accessed itself and its children

readonly,static keywords

modules-- ES6
import and export are keywords in ES6

Type Assertion: sometimes type interferance will not work correct , so at that times we define value as our known data type

Yesterday we discussed,never,enum,interfaces,type alias,class implementation,access modifiers,access specifiers,type Assertion

Advanced Topics:
Generics: Generics are used to define general dat type which can be named while invoking class/function

function fun<P>(a:P):P{}
fun<number>(2)

Declaration Files:
if i'm using any third party libraries, we use declaration files to define data types for 3rd party code

it's extension is .d.ts

namespaces:namespaces are used to group your functionalities. it works while exporting from one file to another file.

Decorators: always we use @ before a  decorator