don't re-run smart interval callback if there is already one in progress

because some things take time

app/assets/javascripts/smart_interval.js

@@ -42,13 +42,16 @@ class SmartInterval {
     const cfg = this.cfg;
     const state = this.state;
 
-    if (cfg.immediateExecution) {
+    if (cfg.immediateExecution && !this.isLoading) {
       cfg.immediateExecution = false;
-      cfg.callback();
+      this.triggerCallback();
     }
 
     state.intervalId = window.setInterval(() => {
-      cfg.callback();
+      if (this.isLoading) {
+        return;
+      }
+      this.triggerCallback();
 
       if (this.getCurrentInterval() === cfg.maxInterval) {
         return;
@@ -76,7 +79,7 @@ class SmartInterval {
 
   // start a timer, using the existing interval
   resume() {
-    this.stopTimer(); // stop exsiting timer, in case timer was not previously stopped
+    this.stopTimer(); // stop existing timer, in case timer was not previously stopped
     this.start();
   }
 
@@ -104,6 +107,17 @@ class SmartInterval {
     this.initPageUnloadHandling();
   }
 
+  triggerCallback() {
+    this.isLoading = true;
+    this.cfg.callback()
+      .then(() => {
+        this.isLoading = false;
+      })
+      .catch(() => {
+        this.isLoading = false;
+      });
+  }
+
   initVisibilityChangeHandling() {
     // cancel interval when tab no longer shown (prevents cached pages from polling)
     document.addEventListener('visibilitychange', this.handleVisibilityChange.bind(this));

app/assets/javascripts/vue_merge_request_widget/mr_widget_options.js

@@ -81,7 +81,7 @@ export default {
       return new MRWidgetService(endpoints);
     },
     checkStatus(cb) {
-      this.service.checkStatus()
+      return this.service.checkStatus()
         .then(res => res.json())
         .then((res) => {
           this.handleNotification(res);
@@ -121,7 +121,7 @@ export default {
       }
     },
     fetchDeployments() {
-      this.service.fetchDeployments()
+      return this.service.fetchDeployments()
         .then(res => res.json())
         .then((res) => {
           if (res.length) {

spec/javascripts/smart_interval_spec.js

@@ -9,7 +9,7 @@ import '~/smart_interval';
 
   function createDefaultSmartInterval(config) {
     const defaultParams = {
-      callback: () => {},
+      callback: () => Promise.resolve(),
       startingInterval: DEFAULT_STARTING_INTERVAL,
       maxInterval: DEFAULT_MAX_INTERVAL,
       incrementByFactorOf: DEFAULT_INCREMENT_FACTOR,