Inspired by JSFuck, but here's the rules:

• 7-bit printable ASCII (32 to 126)
• No alphanumerics ([a-zA-Z0-9]), no spaces, only `` quotes

Use either `${<code>}` or (<code>+[]) to obtain useful keywords:

We can use variables, but only those whose name contains `$` and `_` so we'll use some sort of morse code-based encoding, with `$`⇒`.` and `_`⇒`-`, and a prefix to differentiate lowercase and uppercase:

Actually, we can just use the [a,b]=“ab” notation to make it way shorter. Note that using +[] or +`` is now shorter due to the lack of need of parentheses.

[,$___,$_$$$,$$___,$$,$_$_,$_,____$,____]={}+[],
[$$$_$,$$_,$$_$$,$$$$]=![]+[],
[,$$_$,$$$_]=!``+[],
[__$]=-`!`+[],
[,_$$,$_$,$$$_$,$$$,$_$,,,$_$__]=~[]/[]+[],
[$$$_,,$_$$]=[][[]]+[]

Now we have enough letters to execute arbitrary code:

$=(_=>_)["constructor"] // returns Function

$=(_=>_)[$_$_$+$___+$_$+$$$$+$_+$$_$+$$$_+$_$_$+$_+$___+$$_$]

We can then use `btoa` to get a lot of the letters we're missing:

[K,C,g,h]=Function("return btoa`((!`")() // returns 'KCgh'

[,,$__$,$$$$$]=$($$_$+$$+$_+$$$_+$$_$+$_$+____$+$_$$$+$_+$___+$$_+`\`((!\``)()

_=Function("return this")()

_=$($$_$+$$+$_+$$$_+$$_$+$_$+____$+$_+$$$$$+$$$+$$$$)()

_["console"]["log"]("hello")

_[$_$_$+$___+$_$+$$$$+$___+$$_$$+$$][$$_$$+$___+$__$]($$$$$+$$+$$_$$+$$_$$+$___)

[,$___,$_$$$,$$___,$$,$_$_$,$_,____$,____]={}+[],[$$$_$,$$_,$$_$$,$$$$]=![]+[],[,$$_$,$$$_]=!``+[],[__$]=-`!`+[],[,_$$,$_$,$$$_$,$$$,$_$,,,$_$__]=~[]/[]+[],[$$$_,,$_$$]=[][[]]+[],$=(_=>_)[$_$_$+$___+$_$+$$$$+$_+$$_$+$$$_+$_$_$+$_+$___+$$_$],[,,$__$,$$$$$]=$($$_$+$$+$_+$$$_+$$_$+$_$+____$+$_$$$+$_+$___+$$_+`\`((!\``)(),_=$($$_$+$$+$_+$$$_+$$_$+$_$+____$+$_+$$$$$+$$$+$$$$)(),_[$_$_$+$___+$_$+$$$$+$___+$$_$$+$$][$$_$$+$___+$__$]($$$$$+$$+$$_$$+$$_$$+$___)