I'm surprised by this:

> The "use strict" directive can only be applied to the body of functions with simple parameters. Using "use strict" in functions with rest, default, or destructured parameters is a syntax error.

    function sum(a = 1, b = 2) {
      // SyntaxError: "use strict" not allowed in function with default parameter
      "use strict";
      return a + b;
    }

Not that I would see myself doing this, I would put strict mode in a function containing all the code of the file that does not take any argument (or maybe dependencies), but why would "use strict"; be forbidden here?