Getting error in IE11. No error in other browsers.
For example, using a basic Esri sample below errors in IE.
Same issue in 4.12
Version 3.9 works in IE
// *************************************************
// API loaded in footer...
// *************************************************
function somefunc() {
  try {
    require(["esri/Map", "esri/views/MapView"], function(Map, MapView) {
        var map = new Map({
          basemap: "streets"
        });
        var view = new MapView({
          container: "mapViewer",
          map: map,
          zoom: 4,
          center: [15, 65] // longitude, latitude
        });
    });
  } catch (error) {
    console.log(error);
  }
}
// ****************************
// Error output to console
// ****************************
TypeError: [object Object] is not an object!
 {
 [functions]: ,
 @@hasInstance: undefined,
 @@isConcatSpreadable: undefined,
 @@iterator: undefined,
 @@match: undefined,
 @@observable: undefined,
 @@replace: undefined,
 @@search: undefined,
 @@species: undefined,
 @@split: undefined,
 @@toPrimitive: undefined,
 @@toStringTag: undefined,
 @@unscopables: undefined,
 __proto__: { },
 at Anonymous function (https://js.arcgis.com/4.11/?ver=4.11:429:211)
 at K (https://js.arcgis.com/4.11/?ver=4.11:19:73)
 at K (https://js.arcgis.com/4.11/?ver=4.11:18:398)
 at K (https://js.arcgis.com/4.11/?ver=4.11:18:398)
 at K (https://js.arcgis.com/4.11/?ver=4.11:18:398)
 at K (https://js.arcgis.com/4.11/?ver=4.11:18:398)
 at K (https://js.arcgis.com/4.11/?ver=4.11:18:398)",
 Symbol()_g.hbfjhg26xy3: undefined
 }