ReferenceError: 'Map' is undefined (IE 11 specific bug)

[PieterVDE]

When comparing 2 objects using the module, IE (11) returns an error whilst Chrome and Firefox do not and execute normally.

ReferenceError: 'Map' is undefined

Usage of the module:

return !equals(obj1, obj2);

where obj1 and obj2 look as follows (if they're not null):

{
  prop1: null | {
        prop1: null | int,
        prop2: null | string,
        prop3: null | boolean,
        prop4: null | string
    },
  prop2: same as prop1
}