I am trying to load my selection like the picture below, where the marching ants go around the edges of my object:
However, i only know how to select the whole layer using this code:
doc.selection.selectAll();
Also, i want to contract the selection by a few pixels and paste it into a channel layer. Any help with that would be great but the most important thing is how to load the selection in the first place.
If you look up in the Javascript Scripting Reference document in your Photoshop install directory you'll see that there are a number of methods available on the selection object to do what you need.
var doc = app.activeDocument;
var channelRef = doc.channels.getByName("TestSelection");
doc.selection.load(channelRef, SelectionType.REPLACE);
doc.selection.contract(new UnitValue(20, 'px'));