Sometimes, it is useful to block the
default behaviour of an event.
In the example given below, we want
that no one be able to type anything
in the input. For this, we
create an event listener for a keydown event
for the given input. Then, we block its
default behaviour and now, no one can type
anything inside it.
The preventDefault method blocks the
event's default behaviour. It can be used
on most events. To know whether an event can be
cancelled, check its event.cancelable property.