src/Obs.js
function observeOnce(object, observer, types) {
  function _observer(changes) {
    observer(changes);
    unobserve(object, _observer);
  }
  observe(object, _observer, types);
}
function observeOnce(object, observer, types) {
  function _observer(changes) {
    observer(changes);
    unobserve(object, _observer);
  }
  observe(object, _observer, types);
}
function observeOnce ( object , observer , types ) { function _observer ( changes ) { observer ( changes ) ; unobserve ( object , _observer ) ; } observe ( object , _observer , types ) ; }
Set up an observer and tear it down after the first report
Set up an observer and tear it down after the first report