Outputing characters in JavaScript with only 4 characters:
[
]
+
!
0
+[]
1
+!+[]
2
+!+[]+!![]
3
+!+[]+!![]+!![]
4
+!+[]+!![]+!![]+!![]
5
+!+[]+!![]+!![]+!![]+!![]
6
+!+[]+!![]+!![]+!![]+!![]+!![]
7
+!+[]+!![]+!![]+!![]+!![]+!![]+!![]
8
+!+[]+!![]+!![]+!![]+!![]+!![]+!![]+!![]
9
+!+[]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]
a
[![]+[]][+[]][+!+[]]
c
[[][[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]]+[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]]+[![]+[]][+[]][+!+[]+!![]]+[!![]+[]][+[]][+[]]+[!![]+[]][+[]][+!+[]+!![]+!![]]+[!![]+[]][+[]][+!+[]]]+[]][+[]][+!+[]+!![]+!![]]
d
[[][[]]+[]][+[]][+!+[]+!![]]
e
[!![]+[]][+[]][+!+[]+!![]+!![]]
f
[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]]
i
[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]]
I
[+[[+!+[]]+[!![]+[]][+[]][+!+[]+!![]+!![]]+[+!+[]]+[+[]]+[+[]]+[+[]]]+[]][+[]][+[]]
l
[![]+[]][+[]][+!+[]+!![]]
n
[+[[+!+[]]+[!![]+[]][+[]][+!+[]+!![]+!![]]+[+!+[]]+[+[]]+[+[]]+[+[]]]+[]][+[]][+!+[]]
N
[+[][+[]]+[]][+[]][+[]]
o
[[][[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]]+[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]]+[![]+[]][+[]][+!+[]+!![]]+[!![]+[]][+[]][+[]]+[!![]+[]][+[]][+!+[]+!![]+!![]]+[!![]+[]][+[]][+!+[]]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]+!![]]
r
[!![]+[]][+[]][+!+[]]
s
[![]+[]][+[]][+!+[]+!![]+!![]]
t
[!![]+[]][+[]][+[]]
u
[!![]+[]][+[]][+!+[]+!![]]
v
[[][[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]]+[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]]+[![]+[]][+[]][+!+[]+!![]]+[!![]+[]][+[]][+[]]+[!![]+[]][+[]][+!+[]+!![]+!![]]+[!![]+[]][+[]][+!+[]]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]]
(
[[][[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]]+[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]]+[![]+[]][+[]][+!+[]+!![]]+[!![]+[]][+[]][+[]]+[!![]+[]][+[]][+!+[]+!![]+!![]]+[!![]+[]][+[]][+!+[]]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]]
)
[[][[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]]+[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]]+[![]+[]][+[]][+!+[]+!![]]+[!![]+[]][+[]][+[]]+[!![]+[]][+[]][+!+[]+!![]+!![]]+[!![]+[]][+[]][+!+[]]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]]
{
[[][[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]]+[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]]+[![]+[]][+[]][+!+[]+!![]]+[!![]+[]][+[]][+[]]+[!![]+[]][+[]][+!+[]+!![]+!![]]+[!![]+[]][+[]][+!+[]]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]]
}
[[][[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]]+[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]]+[![]+[]][+[]][+!+[]+!![]]+[!![]+[]][+[]][+[]]+[!![]+[]][+[]][+!+[]+!![]+!![]]+[!![]+[]][+[]][+!+[]]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]]
blank character
[[][[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]]+[[][[]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]]+[![]+[]][+[]][+!+[]+!![]]+[!![]+[]][+[]][+[]]+[!![]+[]][+[]][+!+[]+!![]+!![]]+[!![]+[]][+[]][+!+[]]]+[]][+[]][+!+[]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]+!![]]