regex string contains max one '#'

regex string contains max one '#'

Need regex to match strings by pattern exclude if '#' more then 1 times in
string
var srg = new RegExp(/([a-z0-9#]+[\s])/g);
Strings:
fdsffmsd,fmsd
qwjswkds03sj
ewew
rfekwjkr#jfkdlsf
wiru0ksd#erjk#jkls
#
casdw##kfdl
Result
fdsffmsd,fmsd
qwjswkds03sj
ewew
rfekwjkr#jfkdlsf
wiru0ksd#erjk#jkls
#
casdw##kfdl
Fiddle
Thanks