What are differences between JavaScript and TypeScript concretely ?

Typings, interfaces, classes. Similar to ES6, I suppose.

Typescript is to javascript what sass is to css. In other words, you use typescript to have better code organization/syntax, but it will always end up being converted to javascript. You can't run raw typescript on a browser or a nodejs server.

It's ES6 with static typing like in Java or C# and some other little nice stuff.

I've seen Typescript described as 2 things: a "linter on steroids" and a transpiler. This drives home the point that Typescript just ends up as pure JavaScript, which I've found many people seem to fail to grasp.