[jasode]

>The author never actually says what is so wrong with JavaScript.

The author does but you have to extract it yourself by using some mental subtraction from the sentences he did write:

>[...], TypeScript has all of the benefits of JavaScript (such as they are) while _adding_ a type system that is expressive and powerful. [...] TypeScript leverages the ubiquity of JavaScript while _adding_ all the power of a modern typing system. And that is why you should be using TypeScript instead.

Translation... subtract out the "added modern type system" from Typescript... to reveal his Javascript criticism: "Javascript does not have a modern type system to help catch errors."