Editing TypeScript

==Concept==
TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. TypeScript wird während des Entwicklungsvorgangs mit Hilfe eines '''Transpilers''' (eine Sonderform eines Compilers) in JavaScript übersetzt. The concepts and features below are add-ons to the JavaScript language. The main benefits are:
* TypeScript provides the static type system which provides great help in catching programming errors at compile time.
* Typescript brings Types, Classes, interfaces & modules. it makes the code more maintainable and scalable.
* Typescript comes with several language features. It supports Encapsulation through classes and modules. Supports constructors, properties & functions. It has support for Interfaces. You can make use of Arrow functions or lambdas or anonymous functions.

==Language==

===Statements===
Statements end with a ''';''' but if it is a single line statement it might be ommitted.

===Data Types===
JavaScript has eight data types. The primitive types are 
* number
* string
* boolean
* bigint
* symbol
* undefined, and 
* null. 
Everything else is an object. The TypeScript Type System supports all of them and also brings its own special types. They are '''unknown''', '''any''', '''void''' & '''never'''.
====Type Annotations====
 funcXYZ : <RETURN_TYPE> {
 }
 varXYZ : <TYPE> = ...;

====Union types====
The union types are special. They allow a variable to be of either of two types:
 var x: string | number;

===Variable Declaration===
* let variables are available in block, var variables are available in the function
* see also [https://www.typescriptlang.org/docs/handbook/variable-declarations.html here]
* [[File:TypeScriptVariableDeclaration1.png|400px]]
* <code?</code> after the variable name is short of <code><TYPE>|undefined</code>

===Classes===
* TypeScript offers special syntax for turning a constructor parameter into a class property with the same name and value. If [[TypeScript#Access_Modifier|access modifiers]] there is no need to declare properties
 export class Menu {
   constructor(
     public id: number,
     public parent_id: number,
     public name: string,
     public comment: string
   ) {

===Interfaces===
Typescript uses in interface in multiple ways (s. [https://www.typescriptlang.org/docs/handbook/interfaces.html here]):
* no access modifiers, everything is public
 interface <INTERFACE_NAME> {
 ...
 implements <INTERFACE_NAME>
 ...

===Access Modifier===
* private
* protected
* public

===Generics===

===Functions===

====Function Parameters====
 function doSomething(value: any, options?: <TYPE>) // options parameter is optional

===Decorators===
A Decorator is a special kind of declaration that can be attached to a class declaration, method, accessor, property, or parameter. Decorators use the form <code>@<Expression></code>, where <Expression> must evaluate to a function that will be called at runtime with information about the decorated declaration.

===Non-null assertion/Bang operator===
When you add an exclamation mark after variable/property name, you're telling to TypeScript that you're certain that value is not null or undefined, which prevents the ts2564 compilation error.

===Optional Chaining Operator===
The <code>?.</code> operator always produces the value undefined when it stops descending into a property chain, even when it encounters the value null.

===Import/Export===
Starting with ECMAScript 2015, JavaScript has a concept of [[JScript#Modules|modules]]. TypeScript shares this concept. Each ts-file is javascript module.
 import { ZipCodeValidator } from "./ZipCodeValidator"; // import a single export from a module

==Installation==
 C:\Uwes\Programme\nodejs>npm install -g typescript

==Resources==
* https://www.typescriptlang.org/docs/handbook/typescript-in-5-minutes.html
* [https://www.tektutorialshub.com/typescript-tutorial/ Typescript Tutorial]
* [https://www.typescriptlang.org/play?#code/G4QwTgBAtgpgznEBzGAuOAXMBLAdkiAXggCIAJGAG0oHsIB1GsSgExIgCgBjG3OGyjAB0tJAApYCZDACUHDkA Typescript Playground]