FB未定义javascript错误codeignitor facebook登录

Question

i have a problem , my Facebook login button does not work in some browsers like firefox or on mobile devices and the consolue shows a javascript error fb is not defined i tried fixing many times, read many blogs but failed , can someone sort the issue in my code here is the script i added in view . the error is at the last line of the script

 <script>

  // This is called with the results from from FB.getLoginStatus().
  function statusChangeCallback(response) {

    console.log(response);
    if (response.status === 'connected') {


      testAPI();

    } else {
      // The person is not logged into your app or we are unable to tell.

    }
  }

  // This function is called when someone finishes with the Login
  // Button.  See the onlogin handler attached to it in the sample
  // code below.
  function checkLoginState() {
    FB.getLoginStatus(function(response) {
      statusChangeCallback(response);
    });
  }

  window.fbAsyncInit = function() {
    FB.init({
      appId      : '***********************',
      cookie     : true,  // enable cookies to allow the server to access 
                          // the session
      xfbml      : true,  // parse social plugins on this page
      version    : 'v3.1' // use graph api version 2.8
    });

    // Now that we've initialized the JavaScript SDK, we call 
    // FB.getLoginStatus().  This function gets the state of the
    // person visiting this page and can return one of three states to
    // the callback you provide.  They can be:
    //
    // 1. Logged into your app ('connected')
    // 2. Logged into Facebook, but not your app ('not_authorized')
    // 3. Not logged into Facebook and can't tell if they are logged into
    //    your app or not.
    //
    // These three cases are handled in the callback function.

    FB.getLoginStatus(function(response) {
      statusChangeCallback(response);
    });

  };

  // Load the SDK asynchronously
  (function(d, s, id) {
    var js, fjs = d.getElementsByTagName(s)[0];
    if (d.getElementById(id)) return;
    js = d.createElement(s); js.id = id;
    js.src = "https://connect.facebook.net/en_US/sdk.js";
    fjs.parentNode.insertBefore(js, fjs);
  }(document, 'script', 'facebook-jssdk'));

  // Here we run a very simple test of the Graph API after login is
  // successful.  See statusChangeCallback() for when this call is made.
  function testAPI() {
    //console.log('Welcome!  Fetching your information.... ');
    FB.api('/me?fields=name,email,first_name,last_name', function(response) {
        console.log(response);
        //document.getElementById('status').innerHTML = 'Thanks for logging in, ' + response.email + '!';
        document.getElementById("fbuid").value=response.id;
        document.getElementById("first_name").value=response.first_name;
        document.getElementById("last_name").value=response.last_name;
        document.getElementById("fb_email").value=response.email;
        //if(response.email){
            document.getElementById("fblogin").submit();
        //}
    });
  }

  document.getElementById('test').addEventListener('click', function() {
    //do the login
    FB.login(statusChangeCallback, {scope: 'email,public_profile', 
  return_scopes: true});
}, false);
</script>