diff --git a/.eslintrc b/.eslintrc
index 57a08a065279185a375c539d8ca3641018b87183..aba8112c5a95d026d0ff53b5f02448eab163ce79 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -14,7 +14,8 @@
   "plugins": [
     "filenames",
     "import",
-    "html"
+    "html",
+    "promise"
   ],
   "settings": {
     "html/html-extensions": [".html", ".html.raw", ".vue"],
@@ -26,6 +27,7 @@
   },
   "rules": {
     "filenames/match-regex": [2, "^[a-z0-9_]+$"],
-    "no-multiple-empty-lines": ["error", { "max": 1 }]
+    "no-multiple-empty-lines": ["error", { "max": 1 }],
+    "promise/catch-or-return": "error"
   }
 }
diff --git a/app/assets/javascripts/awards_handler.js b/app/assets/javascripts/awards_handler.js
index f93208944a1ea765e9f08d0a2bc0c6caacb38d32..adb45b0606dd43ac23093774259886b10a41b342 100644
--- a/app/assets/javascripts/awards_handler.js
+++ b/app/assets/javascripts/awards_handler.js
@@ -239,6 +239,9 @@ AwardsHandler
       if (menu) {
         menu.dispatchEvent(new CustomEvent('build-emoji-menu-finish'));
       }
+    }).catch((err) => {
+      emojiContentElement.insertAdjacentHTML('beforeend', '<p>We encountered an error while adding the remaining categories</p>');
+      throw new Error(`Error occurred in addRemainingEmojiMenuCategories: ${err.message}`);
     });
   };
 
diff --git a/app/assets/javascripts/boards/boards_bundle.js b/app/assets/javascripts/boards/boards_bundle.js
index b749ef43cd3bb2258e7107b78a9ac1fdf230bae1..b6dee8177d276e9fb5125d6b356376a76e42148a 100644
--- a/app/assets/javascripts/boards/boards_bundle.js
+++ b/app/assets/javascripts/boards/boards_bundle.js
@@ -1,5 +1,6 @@
 /* eslint-disable one-var, quote-props, comma-dangle, space-before-function-paren */
 /* global BoardService */
+/* global Flash */
 
 import Vue from 'vue';
 import VueResource from 'vue-resource';
@@ -93,7 +94,7 @@ $(() => {
 
           Store.addBlankState();
           this.loading = false;
-        });
+        }).catch(() => new Flash('An error occurred. Please try again.'));
     },
     methods: {
       updateTokens() {
diff --git a/app/assets/javascripts/boards/components/board_list.js b/app/assets/javascripts/boards/components/board_list.js
index adbd82cb687d998d8808d1be8f751ade475981fa..b13386536bf9426daf8278b857807ecc6569e1d5 100644
--- a/app/assets/javascripts/boards/components/board_list.js
+++ b/app/assets/javascripts/boards/components/board_list.js
@@ -57,12 +57,15 @@ export default {
     },
     loadNextPage() {
       const getIssues = this.list.nextPage();
+      const loadingDone = () => {
+        this.list.loadingMore = false;
+      };
 
       if (getIssues) {
         this.list.loadingMore = true;
-        getIssues.then(() => {
-          this.list.loadingMore = false;
-        });
+        getIssues
+          .then(loadingDone)
+          .catch(loadingDone);
       }
     },
     toggleForm() {
diff --git a/app/assets/javascripts/boards/components/modal/index.js b/app/assets/javascripts/boards/components/modal/index.js
index fb0aac3c0e4944519c27acd80ffec20936ad3405..fdab317dc23a493b0f32ee5a84ae65c3d9480bbe 100644
--- a/app/assets/javascripts/boards/components/modal/index.js
+++ b/app/assets/javascripts/boards/components/modal/index.js
@@ -51,11 +51,13 @@ gl.issueBoards.IssuesModal = Vue.extend({
     showAddIssuesModal() {
       if (this.showAddIssuesModal && !this.issues.length) {
         this.loading = true;
+        const loadingDone = () => {
+          this.loading = false;
+        };
 
         this.loadIssues()
-          .then(() => {
-            this.loading = false;
-          });
+          .then(loadingDone)
+          .catch(loadingDone);
       } else if (!this.showAddIssuesModal) {
         this.issues = [];
         this.selectedIssues = [];
@@ -67,11 +69,13 @@ gl.issueBoards.IssuesModal = Vue.extend({
         if (this.$el.tagName) {
           this.page = 1;
           this.filterLoading = true;
+          const loadingDone = () => {
+            this.filterLoading = false;
+          };
 
           this.loadIssues(true)
-            .then(() => {
-              this.filterLoading = false;
-            });
+            .then(loadingDone)
+            .catch(loadingDone);
         }
       },
       deep: true,
diff --git a/app/assets/javascripts/boards/components/new_list_dropdown.js b/app/assets/javascripts/boards/components/new_list_dropdown.js
index 22f20305624f02ecbc9ed97cd0b830cfc530be22..7e3bb79af1d4aaf35514c97a4f74d3d4322dcc82 100644
--- a/app/assets/javascripts/boards/components/new_list_dropdown.js
+++ b/app/assets/javascripts/boards/components/new_list_dropdown.js
@@ -1,4 +1,5 @@
-/* eslint-disable comma-dangle, func-names, no-new, space-before-function-paren, one-var */
+/* eslint-disable comma-dangle, func-names, no-new, space-before-function-paren, one-var,
+   promise/catch-or-return */
 
 window.gl = window.gl || {};
 window.gl.issueBoards = window.gl.issueBoards || {};
diff --git a/app/assets/javascripts/boards/stores/boards_store.js b/app/assets/javascripts/boards/stores/boards_store.js
index 66384d9c03861d74878538c32589489f128864e6..ccb000992155f00120025eac927703058ef08c3d 100644
--- a/app/assets/javascripts/boards/stores/boards_store.js
+++ b/app/assets/javascripts/boards/stores/boards_store.js
@@ -36,6 +36,9 @@ gl.issueBoards.BoardsStore = {
       .save()
       .then(() => {
         this.state.lists = _.sortBy(this.state.lists, 'position');
+      })
+      .catch(() => {
+        // https://gitlab.com/gitlab-org/gitlab-ce/issues/30821
       });
     this.removeBlankState();
   },
diff --git a/app/assets/javascripts/diff_notes/components/resolve_btn.js b/app/assets/javascripts/diff_notes/components/resolve_btn.js
index 8fafd13c6c2700635b137f9c9dade4b5300bd96e..92f6fd654b32e5a9d3df4ac4e3f289815a859202 100644
--- a/app/assets/javascripts/diff_notes/components/resolve_btn.js
+++ b/app/assets/javascripts/diff_notes/components/resolve_btn.js
@@ -64,6 +64,8 @@ const ResolveBtn = Vue.extend({
       });
     },
     resolve: function () {
+      const errorFlashMsg = 'An error occurred when trying to resolve a comment. Please try again.';
+
       if (!this.canResolve) return;
 
       let promise;
@@ -87,10 +89,12 @@ const ResolveBtn = Vue.extend({
           CommentsStore.update(this.discussionId, this.noteId, !this.isResolved, resolved_by);
           this.discussion.updateHeadline(data);
         } else {
-          new Flash('An error occurred when trying to resolve a comment. Please try again.', 'alert');
+          new Flash(errorFlashMsg);
         }
 
         this.updateTooltip();
+      }).catch(() => {
+        new Flash(errorFlashMsg);
       });
     }
   },
diff --git a/app/assets/javascripts/diff_notes/services/resolve.js b/app/assets/javascripts/diff_notes/services/resolve.js
index e1e2e3e93f9b22ef0844d1ba1972ca87fa7a73c0..4ea6ba8a73d8b6f1284c04bb1017e7c64aacf684 100644
--- a/app/assets/javascripts/diff_notes/services/resolve.js
+++ b/app/assets/javascripts/diff_notes/services/resolve.js
@@ -51,8 +51,10 @@ class ResolveServiceClass {
 
         discussion.updateHeadline(data);
       } else {
-        new Flash('An error occurred when trying to resolve a discussion. Please try again.', 'alert');
+        throw new Error('An error occurred when trying to resolve discussion.');
       }
+    }).catch(() => {
+      new Flash('An error occurred when trying to resolve a discussion. Please try again.');
     });
   }
 
diff --git a/app/assets/javascripts/due_date_select.js b/app/assets/javascripts/due_date_select.js
index db10b3839138eae4b4f566cd296602a3a572ca0b..dd95b6530f6cea7e1cca4e0c8e967276929263a6 100644
--- a/app/assets/javascripts/due_date_select.js
+++ b/app/assets/javascripts/due_date_select.js
@@ -115,11 +115,13 @@ class DueDateSelect {
     this.$dropdown.trigger('loading.gl.dropdown');
     this.$selectbox.hide();
     this.$value.css('display', '');
+    const fadeOutLoader = () => {
+      this.$loading.fadeOut();
+    };
 
     gl.issueBoards.BoardsStore.detail.issue.update(this.$dropdown.attr('data-issue-update'))
-      .then(() => {
-        this.$loading.fadeOut();
-      });
+      .then(fadeOutLoader)
+      .catch(fadeOutLoader);
   }
 
   submitSelectedDate(isDropdown) {
diff --git a/app/assets/javascripts/filtered_search/filtered_search_manager.js b/app/assets/javascripts/filtered_search/filtered_search_manager.js
index a5eb33dd9de35aa78ce9f75b4fb1017d74f808d3..68a832102a0afc4e38baf5d4d909cb048735c29e 100644
--- a/app/assets/javascripts/filtered_search/filtered_search_manager.js
+++ b/app/assets/javascripts/filtered_search/filtered_search_manager.js
@@ -343,6 +343,8 @@ class FilteredSearchManager {
         const resultantSearches = this.recentSearchesStore.addRecentSearch(searchQuery);
         this.recentSearchesService.save(resultantSearches);
       }
+    }).catch(() => {
+      // https://gitlab.com/gitlab-org/gitlab-ce/issues/30821
     });
   }
 
diff --git a/app/assets/javascripts/groups_select.js b/app/assets/javascripts/groups_select.js
index 10363c16bae48d8a6a80ba5b9bb55d0231d2714e..acfa4bd4c6b4c25f1b11e63d304a7989f111fa14 100644
--- a/app/assets/javascripts/groups_select.js
+++ b/app/assets/javascripts/groups_select.js
@@ -1,4 +1,8 @@
-/* eslint-disable func-names, space-before-function-paren, no-var, wrap-iife, one-var, camelcase, one-var-declaration-per-line, quotes, object-shorthand, prefer-arrow-callback, comma-dangle, consistent-return, yoda, prefer-rest-params, prefer-spread, no-unused-vars, prefer-template, max-len */
+/* eslint-disable func-names, space-before-function-paren, no-var, wrap-iife, one-var,
+                  camelcase, one-var-declaration-per-line, quotes, object-shorthand,
+                  prefer-arrow-callback, comma-dangle, consistent-return, yoda,
+                  prefer-rest-params, prefer-spread, no-unused-vars, prefer-template,
+                  promise/catch-or-return */
 /* global Api */
 
 var slice = [].slice;
diff --git a/app/assets/javascripts/labels_select.js b/app/assets/javascripts/labels_select.js
index 443fb3e0ca96c183148c2f8f3076b31888495aec..9a60f5464df952782a15c08712e0d1980adb95b3 100644
--- a/app/assets/javascripts/labels_select.js
+++ b/app/assets/javascripts/labels_select.js
@@ -332,6 +332,9 @@
           vue: $dropdown.hasClass('js-issue-board-sidebar'),
           clicked: function(label, $el, e, isMarking) {
             var isIssueIndex, isMRIndex, page, boardsModel;
+            var fadeOutLoader = () => {
+              $loading.fadeOut();
+            };
 
             page = $('body').data('page');
             isIssueIndex = page === 'projects:issues:index';
@@ -396,9 +399,8 @@
               $loading.fadeIn();
 
               gl.issueBoards.BoardsStore.detail.issue.update($dropdown.attr('data-issue-update'))
-                .then(function () {
-                  $loading.fadeOut();
-                });
+                .then(fadeOutLoader)
+                .catch(fadeOutLoader);
             }
             else {
               if ($dropdown.hasClass('js-multiselect')) {
diff --git a/app/assets/javascripts/milestone_select.js b/app/assets/javascripts/milestone_select.js
index 773fe3233a7f522c02250b85431e498ef3e4eafe..bebd0aa357e0e8f79c249d99ab678c6d3983e0a5 100644
--- a/app/assets/javascripts/milestone_select.js
+++ b/app/assets/javascripts/milestone_select.js
@@ -164,6 +164,9 @@
                 .then(function () {
                   $dropdown.trigger('loaded.gl.dropdown');
                   $loading.fadeOut();
+                })
+                .catch(() => {
+                  $loading.fadeOut();
                 });
             } else {
               selected = $selectbox.find('input[type="hidden"]').val();
diff --git a/app/assets/javascripts/monitoring/prometheus_graph.js b/app/assets/javascripts/monitoring/prometheus_graph.js
index d82a4eb96426d9b8930fc4c4221f5cd7df64788e..aff507abb916f39cb63dd3821fc33248bd240dd4 100644
--- a/app/assets/javascripts/monitoring/prometheus_graph.js
+++ b/app/assets/javascripts/monitoring/prometheus_graph.js
@@ -71,6 +71,8 @@ class PrometheusGraph {
         this.transformData(metricsResponse);
         this.createGraph();
       }
+    }).catch(() => {
+      new Flash('An error occurred when trying to load metrics. Please try again.');
     });
   }
 
diff --git a/app/assets/javascripts/users_select.js b/app/assets/javascripts/users_select.js
index 3325a7d429c3bc8d5afee0cb84318202ecd95af4..30902767705c6a4a405b7cb9d918455b251caec9 100644
--- a/app/assets/javascripts/users_select.js
+++ b/app/assets/javascripts/users_select.js
@@ -56,6 +56,9 @@
             gl.issueBoards.BoardsStore.detail.issue.update($dropdown.attr('data-issue-update'))
               .then(function () {
                 $loading.fadeOut();
+              })
+              .catch(function () {
+                $loading.fadeOut();
               });
           };
 
diff --git a/package.json b/package.json
index a17399ddb8f614b897e3d2af9a2e97849ccb97b3..e65f30eea77d072bd5b4c627bec9fc0244d81736 100644
--- a/package.json
+++ b/package.json
@@ -60,6 +60,7 @@
     "eslint-plugin-filenames": "^1.1.0",
     "eslint-plugin-import": "^2.2.0",
     "eslint-plugin-jasmine": "^2.1.0",
+    "eslint-plugin-promise": "^3.5.0",
     "istanbul": "^0.4.5",
     "jasmine-core": "^2.5.2",
     "jasmine-jquery": "^2.1.1",
diff --git a/spec/javascripts/blob/sketch/index_spec.js b/spec/javascripts/blob/sketch/index_spec.js
index 0e4431548c47e8c1aaef58653e8dd6369344458b..79f405598172b4f008aee700407dfb38a0de5739 100644
--- a/spec/javascripts/blob/sketch/index_spec.js
+++ b/spec/javascripts/blob/sketch/index_spec.js
@@ -1,4 +1,4 @@
-/* eslint-disable no-new */
+/* eslint-disable no-new, promise/catch-or-return */
 import JSZip from 'jszip';
 import SketchLoader from '~/blob/sketch';
 
diff --git a/spec/javascripts/filtered_search/services/recent_searches_service_spec.js b/spec/javascripts/filtered_search/services/recent_searches_service_spec.js
index 2a58fb3a7df087cddcfe24762f5fe6c60e1b4e0c..c255bf7c93996d098ef003da486581d19d84ee56 100644
--- a/spec/javascripts/filtered_search/services/recent_searches_service_spec.js
+++ b/spec/javascripts/filtered_search/services/recent_searches_service_spec.js
@@ -1,3 +1,5 @@
+/* eslint-disable promise/catch-or-return */
+
 import RecentSearchesService from '~/filtered_search/services/recent_searches_service';
 
 describe('RecentSearchesService', () => {
diff --git a/spec/javascripts/lib/utils/common_utils_spec.js b/spec/javascripts/lib/utils/common_utils_spec.js
index 56aabc16382e9a41fc5ecaaf97ecd751443221fb..a00efa10119ce4d3a2eae999913a4ae093177385 100644
--- a/spec/javascripts/lib/utils/common_utils_spec.js
+++ b/spec/javascripts/lib/utils/common_utils_spec.js
@@ -1,3 +1,5 @@
+/* eslint-disable promise/catch-or-return */
+
 require('~/lib/utils/common_utils');
 
 (() => {
diff --git a/yarn.lock b/yarn.lock
index e16cd9c36730167a9ef8534fd0e2a393be13c11d..90ba39a32514fbfa8baf3ab4094dd83cc91c033e 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1988,6 +1988,10 @@ eslint-plugin-jasmine@^2.1.0:
   version "2.2.0"
   resolved "https://registry.yarnpkg.com/eslint-plugin-jasmine/-/eslint-plugin-jasmine-2.2.0.tgz#7135879383c39a667c721d302b9f20f0389543de"
 
+eslint-plugin-promise@^3.5.0:
+  version "3.5.0"
+  resolved "https://registry.yarnpkg.com/eslint-plugin-promise/-/eslint-plugin-promise-3.5.0.tgz#78fbb6ffe047201627569e85a6c5373af2a68fca"
+
 eslint@^3.10.1:
   version "3.15.0"
   resolved "https://registry.yarnpkg.com/eslint/-/eslint-3.15.0.tgz#bdcc6a6c5ffe08160e7b93c066695362a91e30f2"