TypeScript: a language for application-scale JavaScript development

Say what you want about whether this is a good idea or not, it is clear at least part of MS is really serious about open source.<p>* TypeScript is under the Apache 2.0 license [1]<p>* Source is available via git on Codeplex [2]<p>* Installation is as easy as <i>npm install -g typescript</i> [3]<p>Extra bonus coolness: They've provided an online playground like jsfiddle! [4].<p>[1]<a href="http://typescript.codeplex.com/license" rel="nofollow">http://typescript.codeplex.com/license</a><p>[2]<a href="http://typescript.codeplex.com/SourceControl/changeset/view/d397c54a55db" rel="nofollow">http://typescript.codeplex.com/SourceControl/changeset/view/...</a><p>[3]<a href="http://www.typescriptlang.org/#Download" rel="nofollow">http://www.typescriptlang.org/#Download</a><p>[4]<a href="http://www.typescriptlang.org/Playground/" rel="nofollow">http://www.typescriptlang.org/Playground/</a>

Awesome, great to see this finally released. I'm a dev in FUSE Labs (<a href="http://fuse.microsoft.com" rel="nofollow">http://fuse.microsoft.com</a>) and we've been dogfooding TypeScript for a while now. I'd be happy to answer any questions about using TypeScript vs vanilla JS, converting a large codebase, etc.

All of these compile-to-JS efforts are great, and as much as I love things like CoffeeScript I have to say I definitely worry about language fragmentation.<p>JavaScript is full of flaws, but its monopoly in the browser space has brought about one intriguing and welcome side-effect: a VERY efficient market for both employers and employees.<p>It's easy to overlook how important this common denominator has been for everyone involved. Employees have a tremendous amount of mobility within the industry: don't like your current JavaScript job? No problem - just about every dot-com needs a JavaScripter. Similarly, companies can today tap into a tremendous pool of JavaScript developers.<p>In today's fast-paced development environment, the ability to hit the ground running is key, and I worry that fragmentation will introduce unnecessary friction in the industry.

It looks <i>really</i> good for a first release. The focus on tooling is IMO the most refreshing thing about the project; the playground is great!<p>I haven't dug much into it yet, but there are a couple of annoyances that i noticed in the playground that i wish will be corrected/alleviated somehow:<p>- The language is not expression-oriented. Once i got used to the "everything is an expression" mindset in languages like CoffeeScript or Ruby (or every functional language that i can think of) it feels quite tedious to "go back" and remember that, no, now the "if" is not an expression any more, you can't return it, or pass it to a function, or assign it to something. You can use the special syntax of the "?:" operator for an if-expression, but there is no equivalent for "switch", or "try", or "for".<p>- The type system doesn't seem to support parametric polymorphism. For example, the type of string[]::map is ((string, number, string[]) =&#62; any, any) =&#62; any[] instead of ((string, number, string[]) =&#62; T, any) =&#62; T[]. So the value ["hello", "world"].map((s) =&#62; s + '!') is of type any[] instead of string[], which would be preferable IMO.

Very interesting. The Apache 2.0 Licence is comforting, makes it worth having a look. The docs are here for anyone interested in the spec:<p><a href="http://typescript.codeplex.com/documentation" rel="nofollow">http://typescript.codeplex.com/documentation</a><p>I like what they've done. Nothing too revolutionary, mostly adding static typing to Javascript without straying to far from the existing (or future) language or increasing the noise significantly.<p>Here's some highlights:<p>* Type inference<p><pre><code> function f() { return "Hello World!"; } </code></pre> Will do the right thing<p>* Explicit Typing<p><pre><code> function f(s: string) { return s; } </code></pre> * 'Ambient Types'<p>To facilitate integration into existing JS libraries or the DOM, TypeScript lets you specify 'placeholders' for variables / classes that the runtime would expect to see e.g.<p><pre><code> declare var document; </code></pre> Almost a kind of dependency injection but also a neat way to manage talking to existing code.<p>* Structural Typing<p>* Classes and Interfaces<p><pre><code> interface BankAccount { balance: number; deposit(credit: number): number; } class CheckingAccount extends BankAccount { constructor(balance: number) { super(balance); } writeCheck(debit: number) { this.balance -= debit; } } </code></pre> * Modules<p><pre><code> module M { var s = "hello"; export function f() { return s; } } </code></pre> * Arrow function expressions<p><pre><code> (x) =&#62; { return Math.sin(x); }</code></pre>

It seems to me that the type checking in TypeScript is extremely limited compared to what the Closure Compiler supports. The examples only show simple `fooInstance : Foo` examples, whereas Closure supports function prototype validation and such, a la C. I will need to see more elaborate examples.<p>Granted, there is no documentation that I could find on the website. I understand that this is a "preview," but I disagree with this way of presenting a tool. When the Closure Library was released, for instance, it was absolutely chock full of API documentation. This is because it was used for real-world projects and extensive docs mattered, even internal to Google.<p>There is a language specification (PDF, in the source tree) which is encouraging, but where's the manual? &#60;<a href="http://www.floopsy.com/post/32453280184/w-t-f-m-write-the-freaking-manual&#62;" rel="nofollow">http://www.floopsy.com/post/32453280184/w-t-f-m-write-the-fr...</a>. The specification is largely a rewording of the ES5 spec with insertions where the typing additions are important. It will take a good bit for the reader to separate the wheat from the chaff, as they say.<p>I have more than a sneaking suspicion that this project is essentially a proof-of-concept, and that it is not heavily used at Microsoft. Do you remember "Microsoft Atlas" in 2006, at the height of the JS DOM Library Wars? In the end, they just pushed their developers to use jQuery with some code generation helpers. Microsoft's open-source track record for JavaScript is not impressive, and I think you'd be a damned fool to invest in this technology for any serious project.

This looks nice. I love the fact that there's no runtime that needs to be included or any overhead when the compiled JS runs.<p>It'd be 100% more useful if it was more aware of nullable types -- as it is, it appears that<p><pre><code> null * 7 </code></pre> compiles without any error messages. If they add a "nullable number" type distinct from "number", I'll be a lot more likely to use it.<p>It also appears that some other things compile that perhaps shouldn't, such as<p><pre><code> 7[2] </code></pre> and<p><pre><code> 7["a"] </code></pre> even though (7).a is equivalent and (correctly) fails to compile.

They've added type annotations to all of jQuery it seems?<p><a href="http://typescript.codeplex.com/SourceControl/changeset/view/d397c54a55db#typings%2fjquery.d.ts" rel="nofollow">http://typescript.codeplex.com/SourceControl/changeset/view/...</a>

This is quite impressive technically, and I think the type-checking feature alone can make it appeal to those making large-scale application in collaborative development environment. I hope this inspires other similar efforts. A quick run-down of features:<p>- It's a superset of JavaScript. So there is no porting effort needed. (With CoffeeScript, you do not need to port if you don't want to.)<p>- compile-time type checking, like type erasure in Java's generics.<p>- module support at the language level. It's very thin. It does not give your AMD or CommonJS module, but you can easily hack around it.<p>- class and inheritance support at the language level. The implementation is very similar to CoffeeScript's.

Weird that I didn't spot a friendly list of features.. seems to have some cool ones, like a shortened function expression (from the doc PDF):<p><pre><code> (x) =&#62; { return Math.sin(x); } </code></pre> and modules, which are implemented using the immediately invoked function expression pattern:<p><pre><code> module M { var s = "hello"; export function f() { return s; } } </code></pre> Syntax seems more clear than CoffeeScript and tool chain will probably shape up better. Looking forward to seeing this get some traction.

This looks great, but the IDE seems to be one of the key features, so we're going to need something other than Visual Studio.<p>EDIT: they've got syntax highlighting for some other editors, but full completion and error reporting is still needed <a href="http://blogs.msdn.com/b/interoperability/archive/2012/10/01/sublime-text-vi-emacs-typescript-enabled.aspx" rel="nofollow">http://blogs.msdn.com/b/interoperability/archive/2012/10/01/...</a>

Favorite part about this, I didn't know it was Microsoft until I scrolled down!

Sublime Text, Vi, Emacs: TypeScript enabled <a href="http://blogs.msdn.com/b/interoperability/archive/2012/10/01/sublime-text-vi-emacs-typescript-enabled.aspx" rel="nofollow">http://blogs.msdn.com/b/interoperability/archive/2012/10/01/...</a>

What about debugging? Thats my biggest problem with coffeescript<p>How do they map errors thrown in the browser, to TypeScript code? If this has things like classes and such, the relationship isnt always going to be 1:1 and debugging can become a nightmare. Part of what makes javascript so great is how easy it is to debug. All these "superset" languages that compile to javascript fail hard @ debug support usually

Like someone else commented in the TC article about Typescript, this Resig quote, changing "Google" for "Microsoft" is relevant:<p><pre><code> "Why is [Microsoft] putting time and effort into changing JavaScript when the DOM is what needs fixing?" </code></pre> <a href="https://twitter.com/jeresig/status/124114331616026624" rel="nofollow">https://twitter.com/jeresig/status/124114331616026624</a>

Can I write my TypeScript in coffeescript?

This seems similar to the type checking and optimization done by Google Closure Compiler?

I've written a lot of JavaScript, including large-scale projects, and never once have thought, "Gee, I wish I had type checking."<p>Haven't we come to a consensus that types are more trouble than they're worth? They hurt clarity and catch few bugs.

On a tangent, does anyone know anything about the in-browser editor they are using for the playground? It seems really slick. The javascript references something called "monaco" and the directories are all prefixed with "vs".<p>The code is hosted on their demo site; /Script/vs/editor/editor.main.js appears to be the main js file and has this notice:<p><pre><code> /*! © Microsoft. All rights reserved. This library is supported for use in Windows Store apps only. Build: 1.0.8514.0.win8_rtm.120711-1900 Version: Microsoft.WinJS.1.0 */</code></pre>

Back in the day, Microsoft would use a strategy called "embrace, extend, extinguish." <a href="http://en.wikipedia.org/wiki/Embrace,_extend_and_extinguish" rel="nofollow">http://en.wikipedia.org/wiki/Embrace,_extend_and_extinguish</a><p>Recently, Microsoft has been pushing Javascript very hard (embrace) and now it looks like they've started the "extend" phase.<p>Luckily, no one really worries about them being able to pull off the "extinguish" part anymore... they just don't have enough market power these days.<p>EDIT: Yes, I conceede the fact that TypeScript is OS probably addresses most of these objections.

Now I want to take an advantage of strict typing at runtime, which is obviously not possible, because instead of standardizing a VM all vendors are doing stupid things like this.

It seems the analyser to infer the types of your vars is fairly easily fooled. The following code compiles, but prints out "Hello undefined":<p><pre><code> interface person{ firstname; lastname; } interface apple{ colour; } function hello(p : person){ alert("hello " + p.firstname); } var aPerson = {firstname: "joe", lastname : "blogs"}; var anApple = {color: "red"}; var foo; if(true){ foo = anApple; } hello(foo);</code></pre>

I will admit MS have impressed me here. The fact they've released TypeScript under an Apache 2.0 licence and put the code up on CodePlex goes to show Microsoft are making strides in the open source community. A big change considering the mentality of MS used to be open source was unsafe and a threat to their dominance in the software industry. The world must be ending: Apple is starting to falter and Microsoft is climbing back to the top.

In case anyones interested, dart JS interop:<p><a href="https://github.com/dart-lang/js-interop/" rel="nofollow">https://github.com/dart-lang/js-interop/</a>

Very good idea. But note that these annotations are just hints : they are enforced only in simple cases :<p>var x = "lol" - error found : <a href="http://pastebin.com/R1wqp0CS" rel="nofollow">http://pastebin.com/R1wqp0CS</a> var x; x = "lol" - accepted : <a href="http://pastebin.com/0vc68RbY" rel="nofollow">http://pastebin.com/0vc68RbY</a>

Codeplex/samples/simple (<a href="http://bit.ly/Svcc4Y" rel="nofollow">http://bit.ly/Svcc4Y</a>) is the same as the CoffeeScript constructors doc section (<a href="http://bitly.com/PnLtGy" rel="nofollow">http://bitly.com/PnLtGy</a>)... Wonder what other stuff they borrowed from CoffeeScript?

Wholeheartedly support this thinking softie has no daggers hidden. The changes do make the language more readable and maintaninable compared to the mess called JavaScript. If the IDE is support is also there, this will be a no-brainer.

(Wikipedia) “Some examples, like Dart, portend that JavaScript has fundamental flaws and to support these scenarios requires a ‘clean break’ from JavaScript in both syntax and runtime. We disagree with this point of view.” - Microsoft’s JavaScript team<p>If Google comes out with Dart, well, then there's no need for that. But it's ok for Microsoft to be secretly working on their own Javascript 2.0. Just sayin' - Why criticize Dart when you've just come with almost the same thing? :)<p>But snark aside, good job Microsoft. Well done.

It's good to see sharp developers like Anders Hejlsberg spearheading this. I really hope this means we'll get LINQ sometime in the future; good to hear generics are on the way.

I worked on a joke/conversion project a little while ago that achieves the same ends without having to compile to JavaScript.<p>The only reason I wrote it was to prove to a co-worker who was "hating" on JavaScript that it IS possible to have a type system in JavaScript - if that's what you want. Its not the same end result but similar enough to warrant a mention.<p>Here's the repo: <a href="https://github.com/christopherdebeer/TypedFunc" rel="nofollow">https://github.com/christopherdebeer/TypedFunc</a>

One of the key TypeScript features is not only the fact that JavaScript program is TypeScript programs but also ability to add type annotations to existing javascript libraries without changing of their source code. For example, see port of Backbone's TodoMVC: <a href="http://typescript.codeplex.com/SourceControl/changeset/view/d397c54a55db#samples%2ftodomvc%2fjs%2ftodos.ts" rel="nofollow">http://typescript.codeplex.com/SourceControl/changeset/view/...</a>

I was reading the synopsis on the page then it faded out and replaced it with sample code. Geez, let me read and then scroll down. WTF is with the carousel non-sense?

They added static typing to javascript, except you can still pass a number to a function that takes a string. In their example <a href="http://www.typescriptlang.org/Playground/" rel="nofollow">http://www.typescriptlang.org/Playground/</a> replace the<p><pre><code> new Greeter("World"); </code></pre> with<p><pre><code> new Greeter(5); </code></pre> and it still works. What good is adding types to functions if they are ignored?

Would it not be just as reasonable to put type information in JSDoc, and build a preprocessor that does the complaining?

So they've set up a site for TypeScript but as far as I can tell, that site hasn't got a blog. With so many projects vying for attention, subscribing to a project's blog is my default way of keeping it in mind for later. If they post interesting updates, I'll be reminded later to come back and give it a closer look.

IMO Microsoft looks for web-developer loyalty because recent stupid policy of big monopoly drive them to zero share on web-browser market. The only remaining question: will IE10 support TypeScript or it will be added in IE11 only?

The only thing that I find "exciting" in the land of compiled-to-javascript languages is LiveScript (<a href="http://gkz.github.com/LiveScript/" rel="nofollow">http://gkz.github.com/LiveScript/</a>)...

I wish they had named it something else. typescript is the default output file name for script(1).<p><a href="http://www.unix.com/man-page/Linux/1/script/" rel="nofollow">http://www.unix.com/man-page/Linux/1/script/</a>

&#62; The scope of a parameter, local variable, or local function declared within a function declaration (including a constructor, member function, or member accessor declaration) or function expression is the body of that function declaration or function expression.<p>This thing claims to be meant for "application-scale" JavaScript, and yet doesn't repair even JavaScript's most notorious error?<p>A suggestion to the authors. Purchase this book:<p><a href="http://www.amazon.com/JavaScript-Good-Parts-Douglas-Crockford/dp/0596517742" rel="nofollow">http://www.amazon.com/JavaScript-Good-Parts-Douglas-Crockfor...</a><p>... then go through the book with a fine-tooth comb, and every time it describes something as a "bad part" or an "awful part", delete or fix that misfeature in TypeScript.

(for posterity, stray duplicate discussion with exactly the same url: <a href="http://news.ycombinator.com/item?id=4597724" rel="nofollow">http://news.ycombinator.com/item?id=4597724</a>)

What unit test framework are they using in the source? It looks like Jasmine ('describe', 'it') but then it has 'assert' and I can't find an include for it.

<p><pre><code> $ t command not found </code></pre> clearly they could have named the compiler just 't' instead of the overly verbose 'tsc'. all those extra characters!!

Looks really good. The IDE support looks like a big bonus. Wish this had been released on a Friday -- have to wait a bit before I can dig deeper!

Am I the only one experiencing sluggish scrolling on that site? Rather ironic for a site boasting about application-scale development.

This looks very good enhancement on top of Javascript. Hope browsers start bundling the TypeScript compiler natively.

yet another language compiled to javascript. What is the deal with the adding type system without doing runtime checks? Does it solve DOM manipulation complexity or it just solve code readability problem? Does it worth to learn new language constructs when you decide to begin low or middle scale projects?

Reminds me about Turbo Pascal, I love it!

Hm.. classes, interfaces... reminds me of AS3; which of course MS stopped becoming the next javascript.<p>Still - looks useful.

The Google guys called. They want Microsoft to stop being jealous of the JS-influenced turd that is Dart.

Not having to deal with types is one of the advantages of JavaScript. This actually makes it worse.

I think javascript is awesome enough so it doesn't need any language improvements. The only improvement over javascript is coffeescript and it's just because its syntax nothing more else. take a look at this video from google i/o: <a href="http://goo.gl/BGvAS" rel="nofollow">http://goo.gl/BGvAS</a>

Could TypeScript be combined with the CoffeeScript syntax to save keystrokes?

Seems pretty cool, but how does it compare to DART or does it even compare?

Why does everyone want to take all the nice features of javascript, it being so loose and freeform and turn it into Java? I don't need interfaces and classes built into the language. That's why it's so powerful and lightweight. Prototypical!<p>People keep making the same mistakes, if you let them.<p>No thanks.

My thoughts on Badass JS here: <a href="http://badassjs.com/post/32674515997/typescript-microsofts-new-typed-javascript-dialect" rel="nofollow">http://badassjs.com/post/32674515997/typescript-microsofts-n...</a>

MS answer to DART?

The compiler's written in... TypeScript!

For stuff like this, you use schema.js.

No list comprehension? No, Thanks.

The lack of strong typing in JavaScript is a <i>feature</i> not a bug.

Looks like all the bad features of Java and JS combined.

lol: application-scale

Open Source? Node.js? Github? Javascript cross-compiler? ES6 based? Type annotations?<p>This is the first sign that they are "getting" 2012 developers and are back in the game with a vengeance. Hope it works.<p>Dart is mid-nineties MS by comparison.

Funny how Microsoft refused ES4 because it came from Macromedia/Adobe ,yet now it pushes a language that looks like its own JScript/AS3

MS has no credibility in this space. If you think slapping an OSS license on their code gives them cred you must be some kind of fanboy. As for Javascript - well, browsers still sucks, webapps still suck, and web development still sucks. Javascript is a big part of that. 30%

<a href="http://i.imgur.com/XB3ib.png" rel="nofollow">http://i.imgur.com/XB3ib.png</a> Oh M$ Oh...