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+---
+language: TypeScript
+contributors:
+    - ["Philippe Vlérick", "https://github.com/pvlerick"]
+filename: learntypescript.ts
+---
+
+TypeScript is a language that aims at easing development of large scale applications written in JavaScript.
+TypeScript adds common concepts such as classes, modules, interfaces, generics and (optional) static typing to JavaScript.
+It is a superset of JavaScript: all JavaScript code is valid TypeScript code so it can be added seamlessly to any project. The TypeScript compiler emits JavaScript.
+
+This article will focus only on TypeScript extra syntax, as oposed to [JavaScript] (../javascript/).
+
+To test TypeScript's compiler, head to the [Playground] (http://www.typescriptlang.org/Playground) where you will be able to type code, have auto completion and directly see the emitted JavaScript.
+
+```ts
+//There are 3 basic types in TypeScript
+var isDone: boolean = false;
+var lines: number = 42;
+var name: string = "Anders";
+
+//..When it's impossible to know, there is the "Any" type
+var notSure: any = 4;
+notSure = "maybe a string instead";
+notSure = false; // okay, definitely a boolean
+
+//For collections, there are typed arrays and generic arrays
+var list: number[] = [1, 2, 3];
+//Alternatively, using the generic array type
+var list: Array<number> = [1, 2, 3];
+
+//For enumerations:
+enum Color {Red, Green, Blue};
+var c: Color = Color.Green;
+
+//Lastly, "void" is used in the special case of a function not returning anything
+function bigHorribleAlert(): void {
+  alert("I'm a little annoying box!");
+}
+
+//Functions are first class citizens, support the lambda "fat arrow" syntax and use type inference
+//All examples are equivalent, the same signature will be infered by the compiler, and same JavaScript will be emitted
+var f1 = function(i: number) : number { return i * i; }
+var f2 = function(i: number) { return i * i; } //Return type infered
+var f3 = (i : number) : number => { return i * i; }
+var f4 = (i: number) => { return i * i; } //Return type infered
+var f5 = (i: number) =>  i * i; //Return type infered, one-liner means no return keyword needed
+
+//Interfaces are structural, anything that has the properties is compliant with the interface
+interface Person {
+  name: string;
+  //Optional properties, marked with a "?"
+  age?: number;
+  //And of course functions
+  move(): void;
+}
+
+//..Object that implements the "Person" interface
+var p : Person = { name: "Bobby", move : () => {} }; //Can be treated as a Person since it has the name and age properties
+//..Objects that have the optional property:
+var validPerson : Person = { name: "Bobby", age: 42, move: () => {} };
+var invalidPerson : Person = { name: "Bobby", age: true }; //Is not a person because age is not a number
+
+//..Interfaces can also describe a function type
+interface SearchFunc {
+  (source: string, subString: string): boolean;
+}
+//..Only the parameters' types are important, names are not important.
+var mySearch: SearchFunc;
+mySearch = function(src: string, sub: string) {
+  return src.search(sub) != -1;
+}
+
+//Classes - members are public by default
+class Point {
+  //Properties
+	x: number;
+	
+	//Constructor - the public/private keywords in this context will generate the boiler plate code
+	// for the property and the initialization in the constructor.
+	// In this example, "y" will be defined just like "x" is, but with less code
+	//Default values are also supported
+	constructor(x: number, public y: number = 0) {
+		this.x = x;
+	}
+	
+	//Functions
+	dist() { return Math.sqrt(this.x * this.x + this.y * this.y); }
+	
+	//Static members
+	static origin = new Point(0, 0);
+}
+
+var p1 = new Point(10 ,20);
+var p2 = new Point(25); //y will be 0
+
+//Inheritance
+class Point3D extends Point {
+	constructor(x: number, y: number, public z: number = 0) {
+		super(x, y); //Explicit call to the super class constructor is mandatory
+	}
+	
+	//Overwrite
+	dist() {
+		var d = super.dist();
+		return Math.sqrt(d * d + this.z * this.z);
+	}
+}
+
+//Modules, "." can be used as separator for sub modules
+module Geometry {
+  export class Square {
+    constructor(public sideLength: number = 0) {
+    }
+    area() {
+      return Math.pow(this.sideLength, 2);
+    }
+  }
+}
+
+var s1 = new Geometry.Square(5);
+
+//..Local alias for referencing a module
+import G = Geometry;
+
+var s2 = new G.Square(10);
+
+//Generics
+//..Classes
+class Tuple<T1, T2> {
+    constructor(public item1: T1, public item2: T2) {
+    }
+}
+
+//..Interfaces
+interface Pair<T> {
+	item1: T;
+	item2: T;
+}
+
+//..And functions
+var pairToTuple = function<T>(p: Pair<T>) {
+	return new Tuple(p.item1, p.item2);
+};
+
+var tuple = pairToTuple({ item1:"hello", item2:"world"});
+
+//Including references to a definition file:
+/// <reference path="jquery.d.ts" />
+
+```
+
+## Further Reading
+ * [TypeScript Official website] (http://www.typescriptlang.org/)
+ * [TypeScript language specifications (pdf)] (http://go.microsoft.com/fwlink/?LinkId=267238)
+ * [Anders Hejlsberg - Introducing TypeScript on Channel 9] (http://channel9.msdn.com/posts/Anders-Hejlsberg-Introducing-TypeScript)
+ * [Source Code on GitHub] (https://github.com/Microsoft/TypeScript)
+ * [Definitely Typed - repository for type definitions] (http://definitelytyped.org/)