What is OS.is_vsync_enabled()?

:information_source: Attention Topic was automatically imported from the old Question2Answer platform.
:bust_in_silhouette: Asked By Apple Horo
:warning: Old Version Published before Godot 3 was released.

Hello there. I’m trying to do the in-game menu for different settings, and one of them is using the vsync.
It works perfectly in the editor, but when I try to run the builded binary, at least on linux, I get the following errors in the console:

SCRIPT ERROR: _ready: Invalid call. Nonexistent function 'is_vsync_enabled' in base 'Object'.
   At: <built-in>:6.
SCRIPT ERROR: save_config: Invalid call. Nonexistent function 'is_vsync_enabled' in base 'Object'.
   At: <built-in>:19.

And 'cause of this, the game fails to save the stuff :<
Is this works how it’s intented to work, or did I miss something.
The code for the scripts is:

extends Button

onready var anim = get_parent().get_node( "anim" );
onready var vsync = OS.is_vsync_enabled();

func _ready():

func update_text():
	if( vsync ):
		set_text( "VSync [X]" );
		set_text( "VSync [ ]" );

func _on_vsync_pressed():
	music.sfx_play( "hit5" );
	vsync = !vsync;
	OS.set_use_vsync( vsync );

func _on_vsync_focus_enter():
	music.sfx_play( "hit1" );


extends Button

onready var anim = get_parent().get_node( "anim" );
var timeout = 1.0;

func _ready():

func _fixed_process( delta ):
	timeout -= delta;
	if( timeout <= 0 ):
		get_tree().change_scene( "res://menu/menu.tscn" );
		set_fixed_process( false );

func save_config():
	var config = ConfigFile.new()
	config.set_value( "video", "fullscreen", OS.is_window_fullscreen() );
	config.set_value( "video", "vsync", OS.is_vsync_enabled() );
	config.set_value( "audio", "sound_volume", AudioServer.get_fx_global_volume_scale() );
	config.set_value( "audio", "music_volume", AudioServer.get_stream_global_volume_scale() );
	config.save( "user://settings.cfg" )

func _on_back_pressed():
	music.sfx_play( "hit5" );
	anim.play( "end" );
	set_fixed_process( true );

func _on_back_focus_enter():
	music.sfx_play( "hit1" );

UPD: also, the At: <built-in>:6. is actually line 4, I just have two empty lines in the beginning of that script, if it has some importance or something