What are the significant differences between TypeScript and Javascript? [closed]

Question

What are the differences between Typescript and Javascript? What are the language design goals of each and how do these design goals differ?

How compatible are libraries and frameworks intended to be used with Javascript, for example jquery, also compatible with Typescript?

Some examples would be helpful.

Answer 1

I've used typescript for a few small hobby projects and I'm convinced that it is the perfect Javascript replacement. My favorite features were:

• Declaration files. With declaration files you can add type informations to your javascript libraries. This structural information will get you fantastic intellisense support in VisualStudio.

• "Standard" OOP. If you come from a C# or Java background you probably won't even need a typescript tutorial. It just works. You have classes, interfaces, access modifiers, extension mechanisms, ...

• Built-in support for modules. Typescript has a slightly confusing module system. You can split your code into several .ts files and just append them but you can also create different modules.

And finally: The syntax. Sometimes it's the small things that have the biggest impact. To me the syntax of typescript feels just perfect. Let me give you a few examples:

Type annotations with ":" and type inference

var a = 5; //infers that a has the type number
var canvas : HTMLCanvasElement = document.getElementById("canvas"); 
// automatically casts to the canvas type. Intellisense will now suggest all the canvas specific methods

Arrays that work as lists, stacks, ...

var array= []; //dynamic type
array.push(1);
array[1]=2;
array.pop();

var array2 : number[] = []; //typed array
array[0]=2;
array[1]="hello"  //compile time error. You've got to love the type system. Finally you can trust your collections

And functions with the arrow syntax as lambdas:

var array=[];
array.push(1);
//...
array.forEach((num)->{alert(num);});
//for single statement functions you can write
array.forEach((num)->alert(num));

Now typed arrays and lambdas combined:

var array: number[]=[];
array.push(1);
//...

//let's assume you want to work with the data in the array. You've got to filter it and process it. Lambdas will come in handy, as well as the type inference
array.filter((num)->num>3).map((num)->num*2).forEach((num)->alert(num));

// the first lambda with the comparison is fully type safe. The compiler knows the type of the array. Therefore it can infer the type of the parameter num and will check if num can be compared to a number

I really enjoyed using typescript. It will significantly increase your productivity. And there's even more to come: http://typescript.codeplex.com/wikipage?title=Roadmap https://github.com/Microsoft/TypeScript/wiki/Roadmap

The 0.9 release will feature generics and for the 1.x versions they plan to implement async/await calls.