/// save:
var data = {
    hp:   global.hp,
    rm:   room,
    px:   obj_player.x,
    py:   obj_player.y,
    coins: global.coins
};
var f = file_text_open_write("save.json");
file_text_write_string(f, json_stringify(data));
file_text_close(f);

/// load:
if (file_exists("save.json")) {
    var f = file_text_open_read("save.json");
    var data = json_parse(file_text_read_string(f));
    file_text_close(f);
    global.hp = data.hp;
    room_goto(data.rm);
}