use native .bind for $bind when js-es >= 5 (#6301)

src/generators/genjs.ml

@@ -1499,7 +1499,11 @@ let generate com =
 	if has_feature ctx "use.$bind" then begin
 		print ctx "var $_, $fid = 0";
 		newline ctx;
-		print ctx "function $bind(o,m) { if( m == null ) return null; if( m.__id__ == null ) m.__id__ = $fid++; var f; if( o.hx__closures__ == null ) o.hx__closures__ = {}; else f = o.hx__closures__[m.__id__]; if( f == null ) { f = function(){ return f.method.apply(f.scope, arguments); }; f.scope = o; f.method = m; o.hx__closures__[m.__id__] = f; } return f; }";
+		(if ctx.es_version < 5 then
+			print ctx "function $bind(o,m) { if( m == null ) return null; if( m.__id__ == null ) m.__id__ = $fid++; var f; if( o.hx__closures__ == null ) o.hx__closures__ = {}; else f = o.hx__closures__[m.__id__]; if( f == null ) { f = function(){ return f.method.apply(f.scope, arguments); }; f.scope = o; f.method = m; o.hx__closures__[m.__id__] = f; } return f; }"
+		else
+			print ctx "function $bind(o,m) { if( m == null ) return null; if( m.__id__ == null ) m.__id__ = $fid++; var f; if( o.hx__closures__ == null ) o.hx__closures__ = {}; else f = o.hx__closures__[m.__id__]; if( f == null ) { f = m.bind(o); o.hx__closures__[m.__id__] = f; } return f; }"
+		);
 		newline ctx;
 	end;
 	if has_feature ctx "use.$arrayPush" then begin