enum E { a, b, c }

var a: any;
var b: number;
var c: E;

var x1: any;
x1 **= a;
x1 **= b;
x1 **= c;
x1 **= null;
x1 **= undefined;

var x2: number;
x2 **= a;
x2 **= b;
x2 **= c;
x2 **= null;
x2 **= undefined;

var x3: E;
x3 **= a;
x3 **= b;
x3 **= c;
x3 **= null;
x3 **= undefined;