Let's say we have the
grade and nationality
of a student
and we need to display
"You get a 10% discount on your course fee"
for any value of student.grade
other than "D".
The condition
!(student.grade === "D")
in the example above,
is logically correct.
However, we should prefer
using the !== operator
for such conditions,
where there is only
one expression in the condition
as shown in the example below.
Let's say we need to display
"You get a 10% discount on your course fee"
when student.grade is not "D"
and
student.nationality is not "India".
Since we need to make
two comparisons here,
it is fine to use the
! operator
as shown below.