add intro

Author: filipesilva

public/docs/_examples/cb-ts-to-js/js-es6-decorators/.babelrc

@@ -3,4 +3,4 @@
     "es2015",
     "angular2"
   ]
-}
+}

public/docs/js/latest/cookbook/ts-to-js.jade

@@ -16,6 +16,8 @@ include ../../../../_includes/_util-fns
 :marked
   ## Table of contents
 
+  [From TS to ES6 to ES5](#from-ts)
+
   [Modularity: imports and exports](#modularity)
 
   [Classes and Class Metadata](#class-metadata)
@@ -29,6 +31,35 @@ include ../../../../_includes/_util-fns
   **Run and compare the live <live-example name="cb-ts-to-js">TypeScript</live-example> and <live-example name="cb-ts-to-js" lang="js">JavaScript</live-example>
   code shown in this cookbook.**
 
+a(id="from-ts")
+.l-main-section
+:marked
+  ## From TS to ES6 to ES5
+  
+  Since TypeScript is a superset of ES6 Javascript, and ES6 itself is a superset of ES5, the 
+  transformation of Typescript code all the way to ES5 javascript can be seen as "shedding"
+  features.
+
+  When going from TypeScript to ES6 with decorators, we mostly remove 
+  [type annotations](https://www.typescriptlang.org/docs/handbook/basic-types.html) 
+  , such as `string` or `boolean`, and
+  [class property modifiers](http://www.typescriptlang.org/docs/handbook/classes.html#public-private-and-protected-modifiers)
+  such as `public` and `private`. 
+  The exception is type annotations used for dependency injection, which can be kept.
+
+  Going from ES6 with decorators to plan ES6 Javascript we lose all 
+  [decorators](https://www.typescriptlang.org/docs/handbook/decorators.html)
+  the remaining type annotations.
+  We also lose class properties, which now have to be declared in the class constructor.
+
+  Finally, in the transition from ES6 to ES5 Javascript the main missing features are `import`
+  statements and `class` declarations. 
+
+  For ES6 transpilation we recommend using a similar setup as our TypeScript quickstart, 
+  replacing TypeScript with [Babel](https://babeljs.io/) using the `es2015` preset. 
+  To use decorators and annotations with Babel, install the 
+  [`angular2`](https://github.com/shuhei/babel-plugin-angular2-annotations) preset as well. 
+
 a(id="modularity")
 .l-main-section
 :marked