on start:

window.fbAsyncInit = function () {
    FB.init({
      appId: FB_APP_ID,
      status: true,
      cookie: true,
      oauth: true,
      xfbml: true
    });
    FB.Event.subscribe("auth.login", function (a) {
        uid = a.authResponse.userID;
      accessToken = a.authResponse.accessToken;
    });
    FB.getLoginStatus(function (a) {
      if (a.status === "connected") {
        uid = a.authResponse.userID;
        accessToken = a.authResponse.accessToken;

        fb_loginok()
      }
    });
  };

  (function (a) {
    var b, c = "facebook-jssdk";
    if (a.getElementById(c)) {
      return
    }
    b = a.createElement("script");
    b.id = c;
    b.async = true;
    b.src = "//connect.facebook.net/en_US/all.js";
    a.getElementsByTagName("head")[0].appendChild(b)
  })(document);

to make the post i use:

FB.api("/" + FB_PAGE_ID + "/feed", "post", {
    message: "test"
 }, function (a, b, c) {
   if (!a || a.error) {} else {
     dosomething();
   }
}