从AJAX代码正确地将值传递给PHP

So I'm trying to pass a value from my AJAX code to my PHP code which connects to an API to get the weather. It works when just using PHP, but I want ajax to return the results to some div on the same page. My code looks correct when I compare it to other examples but it just doesn't work.

Code may not be written with security in mind, standard practice etc, I'm just trying to play around with API's and get the basics of AJAX. api.php:

  $city = $_POST['city'];

  function getCityLat($x) {
    $latUrl = 'https://maps.googleapis.com/maps/api/geocode/json?address='. $x .'APIKEY';

    $latResponse = file_get_contents($latUrl);
    $latArray = json_decode($latResponse, true);

    $lat = $latArray['results'][0]['geometry']['location']['lat'];
echo $lat;
    return $lat;
  }

  function getCityLng($y) {
    $lngUrl = 'https://maps.googleapis.com/maps/api/geocode/json?address='. $y .'APIKEY';

    $lngResponse = file_get_contents($lngUrl);
    $lngArray = json_decode($lngResponse, true);

    $lng = $lngArray['results'][0]['geometry']['location']['lng'];

    echo $lng;
    return $lng;
  }

  function getWeather($x, $y) {
    $weatherUrl = 'https://api.darksky.net/forecast/APIKEY/' . $x . ',' . $y;
    $weatherResponse = file_get_contents($weatherUrl);

    $weatherArray = json_decode($weatherResponse, true);

    $timeZone = $weatherArray['timezone'];
    $locWeather = $weatherArray['currently']['temperature'];
    $locFeelsLike = $weatherArray['currently']['apparentTemperature'];
    $windSpeed = $weatherArray['currently']['windSpeed'];
    $weatherSummary = $weatherArray['currently']['summary'];
    $time = $weatherArray['currently']['time'];

    $outputweather = '<p>Temp: '.$locWeather.'</p>';
    echo $outputweather;
  }

  getWeather(getCityLat($city), getCityLng($city));

?>

index.php(html):

<h3 align="center">Weather</h3>
    <form align="center" method="POST">
      <input type="text" id="city" name="city" placeholder="Enter City">
      <button class="btn btn-xs btn-success" name="city_go" id="city_go">Go</button>
    </form>
  <div id="weather"></div>

JQuery:

function getWeather(city) {
    $.ajax({
      url: "api.php",
      method: "POST",
      data: {city:city}, 
      dataType: "text",
      success: function(data) {
        $('#weather').html(data);
      }
    });
  }

   $(document).on('click', '#city_go', function() {
    var city = $('#city').val();
    getWeather(city);
  });

The problem is that you are submitting a form, which forces a page refresh. Everything else is working correctly, just the page is being refreshed. To fix that you need to update your click event to something like

$(document).on('click', '#city_go', function(e) {
    e.preventDefault();
    var city = $('#city').val();
    getWeather(city);
});

the preventDefault() call will cancel the default action of the form (the page refresh) and allow the AJAX call to follow through and display the data.