Adds requested section, closes #3928

Author: JJ

doc/Language/js-nutshell.pod6

@@ -340,6 +340,21 @@ say 1 +^ 1; # OUTPUT: 0
 say +^1;    # OUTPUT: -2
 =end code
 
+=head3 Checking for definedness
+
+Javascript includes a nullish coalescing operator, C<||>, which progresses
+only if null or undefined:
+
+=for code :lang<javascript>
+undefined || null || 0 || 1 ;   // => 1
+undefined ?? null ?? 0 ?? 1 ;   // => 0
+
+This is very similar to Raku L<C<//>|/routine/$SOLIDUS$SOLIDUS> operator:
+
+=for code
+(Any) || Nil || 0 || 1 ;   # => 1
+(Any) // Nil // 0 // 1 ;   # => 0
+
 =head3 Custom operators and operator overloading
 
 Node.js does not allow operator overloading without having to use a Makefile or