Without any further explanation - look at the code
ক = '' // empty string
খ = !ক + ক // "true"
গ = !খ + ক // "false"
ঘ = ক + {} // "[object Object]"
ঙ = খ[ক++] // "t" = "true"[0]
চ = খ[জ = ক] // "r" = "true"[1]
ছ = ++জ + ক // 2, 3
ঝ = ঘ[জ + ছ] // "c"
খ[
ঝ += // "c"
ঘ[ক] + // "o" = "object"[0]
(খ.গ+ঘ)[ক] + // "n" = "undefined"[1]
গ[ছ] + // "s" = "false"[3]
ঙ + // "t"
চ + // "r"
খ[জ] + // "u" = "true"[2]
ঝ + // "c" = "[object]"[5]
ঙ + // "t"
ঘ[ক] + // "o" = "[object]"[1]
চ // "r"
][
ঝ // "constructor"
](
গ[ক] + // "a"
গ[জ] + // "l"
খ[ছ] + // "e"
চ + // "r"
ঙ + // "t"
"(ক)" // "(1)"
)()
And minified final JS for alert(1) with obfuscation
ক="",খ=!ক+ক,গ=!খ+ক,ঘ=ক+{},ঙ=খ[ক++],চ=খ[জ=ক],ছ=++জ+ক,ঝ=ঘ[জ+ছ],খ[ঝ+=ঘ[ক]+(খ.গ+ঘ)[ক]+গ[ছ]+ঙ+চ+খ[জ]+ঝ+ঙ+ঘ[ক]+চ][ঝ](গ[ক]+গ[জ]+খ[ছ]+চ+ঙ+"(ক)")();