信息窗口的内容是异步添加到DOM的，因此直到

The content of the infowindow is added to the DOM asynchronously, so it can't be found until the InfoWindow "domready" event fires.

从该文档):

准备就绪 |参数:无
当包含InfoWindow的内容附加到DOM时，将引发此事件.如果您正在动态构建信息窗口内容，则可能希望监视此事件.

要将事件侦听器附加到这些按钮，请运行JQuery代码以在"domready"事件侦听器中查找它们:

To attach event listeners to those buttons, run the JQuery code to look for them in a 'domready' event listener:

google.maps.event.addListener(marker, 'click', function() {
  infoWindow.setContent(contentString);
  infoWindow.open(map, this);
  // wait for the infowindow's domready event
  google.maps.event.addListenerOnce(infoWindow, 'domready', function() {
    // find the elements with the "btn" class and add the click listener to the one with id="btnDirection"
    var btn = $(".btn").filter('#btnDirection');
    if (btn != null) {
      for (var i = 0; i < btn.length; i++) {
        btn[i].addEventListener('click', function() {
          console.log("hello")
        });
      };
    };
  });
});

概念提琴证明

代码段:

var geocoder;
var map;

function initialize() {
  var map = new google.maps.Map(
    document.getElementById("map_canvas"), {
      center: new google.maps.LatLng(37.4419, -122.1419),
      zoom: 13,
      mapTypeId: google.maps.MapTypeId.ROADMAP
    });
  var infoWindow = new google.maps.InfoWindow();
  var contentString = '<div id="other"></div><br></br>' +
    '<button type="button" class="btn btn-success" id="btnDirection">Get direction</button> </div>' +
    '<button type="button" class="btn btn-success" id="btnDiscount">Related discount</button> </div>';

  var marker = new google.maps.Marker({
    map: map,
    animation: google.maps.Animation.DROP,
    position: map.getCenter(), // place.geometry.location,
  });

  google.maps.event.addListener(marker, 'click', function() {
    infoWindow.setContent(contentString);
    infoWindow.open(map, this);
    // wait for the infowindow's domready event
    google.maps.event.addListenerOnce(infoWindow, 'domready', function() {
      // find the elements with the "btn" class and add the click listener to the one with id="btnDirection"
      var btn = $(".btn").filter('#btnDirection');
      if (btn != null) {
        for (var i = 0; i < btn.length; i++) {
          btn[i].addEventListener('click', function() {
            document.getElementById("other").innerHTML = "Get Direction was CLICKED";
            console.log("hello")
          });
        };
      };
    });
  });
}
google.maps.event.addDomListener(window, "load", initialize);

html,
body,
#map_canvas {
  height: 100%;
  width: 100%;
  margin: 0px;
  padding: 0px
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://maps.googleapis.com/maps/api/js"></script>
<div id="map_canvas"></div>