Does TypeScript forbid using JavaScript features? no.
Can TypeScript realistically verify that your program is type-safe? no.
Is TypeScript 100% type-safe? no. They wanted fast adoption, therefore they allowed JavaScript and untyped variables.
I have 100% type safety, and it's all done by TypeScript and my programming language IS TypeScript (not JS)
The the final output format generated by a compiler has absolutely nothing to do with whether the Language being compiled is typesafe or not. That would be like saying since Bytecode is not typesafe therefore Java is not a type safe language.
Google closure compiler and JetBrains IDEs can use JSdoc to validate types. I have used those to a reasonable level of accuracy to document entire JavaScript projects where I cannot migrate to TypeScript.
However this is also simultaneously true: You can code in TypeScript and achieve 100% type safety by putting types on everything. If I claim all cubes can be painted red, you can't disprove that by proving green cubes exist.