17   const document = new EventTarget();  constant
28   document.addEventListener('test', handler_once, { once: true });
29   document.addEventListener('test', handler_normal);
30   document.dispatchEvent(new Event('test'));
36   document.dispatchEvent(new Event('test'));
39   document.removeEventListener('test', handler_normal);
45   const document = new EventTarget();  constant
50   document.addEventListener('test', handler, { once: true });
51   document.addEventListener('test', handler);
52   document.dispatchEvent(new Event('test'));
56   document.dispatchEvent(new Event('test'));
60   document.addEventListener('test', handler, { once: true });
61   document.removeEventListener('test', handler);
62   document.dispatchEvent(new Event('test'));
69   const document = new EventTarget();  constant
74       document.dispatchEvent(new Event('test'));
76   document.addEventListener('test', handler, { once: true });
77   document.dispatchEvent(new Event('test'));
84       document.addEventListener('test', handler2, { once: true });
86       document.dispatchEvent(new Event('test'));
88   document.addEventListener('test', handler2, { once: true });
89   document.dispatchEvent(new Event('test'));