// Move cursor to left, or -1 from selection.
// カーソルを左へ移動（選択範囲を1減）

var range = getSelectedRange();

if ( isSelect() === true ) {
  setSelectedRange( range[0], range[1] - 1 );
} else {
  setSelectedRange( range[0] - 1, 0 );
}

function isSelect() {
  if ( getSelectedText().length > 0 ) {
    return true;
  } else {
    return false;
  }
}