Skip adding a layer if the Map Service is down?

[BrettGreenfield__DNR_]

I've got a web map that consumes a number of map services.  Most are hosted on our internal server, but a couple are hosted externally.  One particular service tends to go down somewhat regularly, and when this happens the map itself breaks (not entirely, but it loses enough functionality to be a problem).

Outside of manually checking the web map every morning, I have absolutely no idea how to deal with this.  What usually happens is the service goes down in the middle of the day, we have a complaint from a customer, and I have to manually update the code to skip adding that service to the map until I get word that the service is back up.  Is there a better way of handling this?  Some way to use JS to check to see if the service is up and running before attempting to add the service?

Thanks in advance!

[RobertScheitlin__GISP]

Brett,

  Sure you would use esriRequest to get the json of the map service url and if that esriRequest fails then you do not add that service layer.

[JeffJacobson]

<script src="//cdn.polyfill.io/v2/polyfill.min.js?features=default,Promise"></script>

var sampleUrl = "//services.arcgisonline.com/ArcGIS/rest/services/Reference/World_Transportation/MapServer";
var badUrl = "//services.arcgisonline.com/ArcGIS/rest/services/Reference/FakeService/MapServer"

/**
 * Tests a URL
 * @param {string} url
 * @returns {Promise}
 */
function testService(url) {
  return new Promise(function(resolve, reject) {
    var request = new XMLHttpRequest();
    request.open("get", url + "?f=json");
    request.onloadend = function() {
        if (this.status !== 200) {
          reject({error: this.status});
      } else {
          var response = JSON.parse(this.response);
        if (response.error) {
            reject(response);
        } else {
            resolve(response);
        }
      }
    }
    request.send();
  });
}

[sampleUrl, badUrl].forEach(function(url) {
  testService(url).then(function(response) {
    console.debug(response)
  }, function(error){
    console.error(error);
  });
});