One of the very useful things Typescript has for a dynamic-language-turned-static is smart casts, union types and dependent types union types. Things like these are possible:

    type Animal =
      {
         type: "Dog"
         dogtag: string
         name: string
      } | {
         type: "Cat"
         name: string
         allowedOutside: boolean
      }


      function f(a: Animal) {
          console.log(a.name) // always allowed
          console.log(a.dogtag) // compile error
          if(a.type === "Dog") {
              console.log(a.dogtag) // Allowed
          }
      }

I believe Typescript is fairly unique in this capability.