This is very easy and a perfectly valid question. PhotoShop can crop to selection with a function.

cropToSelection();


// crop to selection
function cropToSelection()
{
  executeAction( charIDToTypeID( "Crop" ), new ActionDescriptor(), DialogModes.NO );
}

But if you want the selection bounds coordinates then use:

var lb = get_selection_bounds();

// alerts current selection bounds
alert(lb[0] + ", " + lb[1] + ", " + lb[2] + ", " + lb[3] );


// function GET SELECTION BOUNDS ()
// ----------------------------------------------------------------
function get_selection_bounds()
{
  // Only works with a selection
  var x = parseFloat(app.activeDocument.selection.bounds[0]);
  var y = parseFloat(app.activeDocument.selection.bounds[1]);
  var x1 = parseFloat(app.activeDocument.selection.bounds[2]);
  var y1 = parseFloat(app.activeDocument.selection.bounds[3]);

  // return the results as an array
  return [x, y, x1, y1];
}