It would be nice to have some examples of what these terms mean, for type system dilletantes like me. I must say, I was a little lost :)

Re: TypeScript:

> TypeScript challenges the status quo, claiming that lowering the cognitive overhead of using types is more important than type soundness. They argue that JavaScript programmers, their main audience, would find it easier to use TypeScript if they deviated from traditional norms.

Im not sure about the official mission statement, but as far as I understand, the purpose of their typesystem is to allow static description of the way existing JavaScript is typed, de facto, in the wild. This explains why e.g. literal strings are a type so you can do:

    interface Eventor {
        on('foo', FooHandler);
        on('bar', BarHandler);
    }

Not because it’s nice to have a type that "foo" satisfies and not "bar", but because there is actual code out there that does this, today. Same for structural typing (TypeScript would be absolute horror to interface with existing code without it). And, I assume, covariant arrays.

TypeScript was not created in a void, as a fresh, new typesystem. It was created to formalise the way existing JavaScript was informally typed. It would have been nice to see a little reference to or acknowledgement of this.

Or an example of how this could have been achieved better; preserving type soundness.