Javascript is,

1. Dynamically strongly typed, but typing is limited to primitive types. 2. So actually it's untyped for objects which is really needs type information. 3. As it lacks class/interface concept at all, type (an)notation is fundamentally impossible, type tracking is also impossible. 4. So lacks ability to offer type information to toolset.

You don't have automated tooling support on Javascript about type, and it will degrade your productivity. So big companies interested on JS platform, are all offering JS with type notation -

1. Google = Dart, 2. MS = TypeScript, 3. Mozilla = Emscripten(in very unique way!)

Javascript is typically described as weakly typed; e.g., "2" + 2 is valid Javascript.