Well jsHint is mistaken here. That's
t /= d / 2
which means
t = t / (d / 2)
Note that the parentheses are important in the alternative version, because normally the /
operator binds left-to-right. The /=
operator is of lower precedence than /
.
Anyway the value of the whole thing will be the resulting (updated) value of "t".
Now, in a larger sense, jsHint might be right to complain about the obscurity of that, but that's a matter of style. The operator-assignment operators are a fairly old tradition, dating back at least to C.