The conversion of the 20,000 lines of legacy Javascript in the Windows Control Library was a success.  I touched on the major issues in my previous posts.   The issues encountered themselves weren’t any kind of flaw in TypeScript,  it just demonstrated the need to keep in mind the style of Javascript code that is being generated.  After going through the experience, the following steps are what I would recommend for TypeScript conversion:

1) Rename your .js (Javascript) files to .ts (TypeScript) files and compile.  Fix all errors that arise and test your fixes.

2) Add type annotations to all variable and parameter declarations.  Minimize the use of the ‘any’ type.  Add interfaces to define function signatures.  Use interfaces to describe existing data structures.  Don’t refactor any of your code yet, wait until conversion is complete.

3) Restructure your JavaScript code into modules and classes.  I myself did Step 3 before Step 2, but if I did it again I would do Step 2 first.