Return Promise for Osmose string requests

modules/services/osmose.js

@@ -174,15 +174,14 @@ export default {
     return jsonPromise(url, cacheDetails).then(() => issue);
   },
 
-  loadStrings(callback, locale=currentLocale) {
+  loadStrings(locale=currentLocale) {
     const items = Object.keys(qaServices.osmose.icons);
 
     if (
       locale in _cache.strings
       && Object.keys(_cache.strings[locale]).length === items.length
     ) {
-        if (callback) callback(null, _cache.strings[locale]);
-        return;
+        return Promise.resolve(_cache.strings[locale]);
     }
 
     // May be partially populated already if some requests were successful
@@ -243,9 +242,7 @@ export default {
       return jsonPromise(url, cacheData);
     });
 
-    Promise.all(allRequests)
-      .then(() => { if (callback) callback(null, _cache.strings[locale]); })
-      .catch(err => { if (callback) callback(err); });
+    return Promise.all(allRequests).then(() => _cache.strings[locale]);
   },
 
   getStrings(itemType, locale=currentLocale) {

modules/svg/osmose.js

@@ -59,20 +59,14 @@ export function svgOsmose(projection, context, dispatch) {
 
   // Enable the layer.  This shows the markers and transitions them to visible.
   function layerOn() {
-    // Strings supplied by Osmose fetched before showing layer for first time
-    // NOTE: Currently no way to change locale in iD at runtime, would need to re-call this method if that's ever implemented
-    // FIXME: If layer is toggled quickly multiple requests are sent
-    // FIXME: No error handling in place
-    getService().loadStrings(editOn);
+    editOn();
 
     drawLayer
       .style('opacity', 0)
       .transition()
       .duration(250)
       .style('opacity', 1)
-      .on('end interrupt', () => {
-        dispatch.call('change');
-      });
+      .on('end interrupt', () => dispatch.call('change'));
   }
 
   // Disable the layer.  This transitions the layer invisible and then hides the markers.
@@ -223,7 +217,12 @@ export function svgOsmose(projection, context, dispatch) {
 
     _layerEnabled = val;
     if (_layerEnabled) {
-      layerOn();
+      // Strings supplied by Osmose fetched before showing layer for first time
+      // NOTE: Currently no way to change locale in iD at runtime, would need to re-call this method if that's ever implemented
+      // FIXME: If layer is toggled quickly multiple requests are sent
+      getService().loadStrings()
+        .then(layerOn)
+        .catch(err => {}); // FIXME: Handle failed json request gracefully in some way
     } else {
       layerOff();
       if (context.selectedErrorID()) {