OpenLayers3 add map to bottom of a layer?

Question

According to OpenLayers 3 documentation, the function

addLayer(layer)

Adds the given layer to the top of this map.

How can I add a layer to the bottom of a map?

P.S. I need this to add a background layer similar to a base layer in OpenLayers 2.

Answer 1

It seems that I found a solution after some trial and error, i.e. simply use a map's layers collection, and insert layer to the head position:

var layers = map.getLayers();
layers.insertAt(0,layer);