Why is ArcGIS API for JavaScript Map.setExtent snapping my extent?

Question

I'm having some problems setting the Map extent using ArcGIS API for JavaScript 3.18.

Whenever I call setExtent with myExtent, the Map ends up at some extent that is close to, but significantly different than myExtent. For example I call setExtent with:

myExtent = Object {type: "extent", xmin: -13486723.42416174, ymin: 6046817, xmax: -11828314.857440159, ymax: 8563452}

Then I handle the extent-change event to log the actual extent:

actualExtent = Object {type: "extent", xmin: -13334853.828803658, ymin: 6277279.110955888, xmax: -11980184.45279824, ymax: 8332989.889044112}

In this example the actualExtent is significantly more zoomed in than myExtent. But sometimes it's more zoomed out, sometimes it's more north, etc. Basically the Map seems to be snapping myExtent to certain zoom levels and positions.

Our server is ArcGIS Server 10.4.1. I have an ArcGIS API for Silverlight client connected to the same server doing the same work but it doesn't have this snapping problem. Can anyone suggest why this is happening and how to stop it?

UPDATE: To clarify how I build and set myExtent, it goes a little like this:

let myExtent = angular.copy(this.map.extent);
myExtent.xmin = -13486723.42416174;  // calculated
myExtent.ymin = 6046817;  // calculated
myExtent.xmax = -11828314.857440159;  // calculated
myExtent.ymax = 8563452;  // calculated
this.map.setExtent(myExtent);

Answer 1

If you'd like a guarantee that the input extent will be shown completely on the map when calling setExtent() you should pass the value true as the second (optional) fit parameter.

map.setExtent(myExtent, true);

https://developers.arcgis.com/javascript/3/jsapi/map-amd.html#setextent