diff --git a/app/assets/javascripts/mumuki_laboratory/application/bridge.js b/app/assets/javascripts/mumuki_laboratory/application/bridge.js
index 63b01a84c..7e2f9efe3 100644
--- a/app/assets/javascripts/mumuki_laboratory/application/bridge.js
+++ b/app/assets/javascripts/mumuki_laboratory/application/bridge.js
@@ -1,60 +1,41 @@
 /**
- * @typedef {{status: string, test_results: [{status: string, title: string}]}} ClientResult
+ * @typedef {"errored"|"failed"|"passed_with_warnings"|"passed"|"pending"|"aborted"} SubmissionStatus
  */
 
 /**
- * @typedef {{solution: object, client_result?: ClientResult}} Submission
+ * @typedef {{
+ *  status: SubmissionStatus,
+ *  test_results: [{status: SubmissionStatus, title: string}]
+ * }} SubmissionClientResult
  */
 
-var mumuki = mumuki || {};
-
-(function (mumuki) {
-  var lastSubmission = {};
-
-  function Laboratory(exerciseId){
-    this.exerciseId = exerciseId;
-  }
-
-  function asString(json){
-    return JSON.stringify(json);
-  }
-
-  function sameAsLastSolution(newSolution){
-    return asString(lastSubmission.content) === asString(newSolution);
-  }
-
-  function lastSubmissionFinishedSuccessfully(){
-    return lastSubmission.result && lastSubmission.result.status !== 'aborted';
-  }
-
-  function sendNewSolution(submission){
-    var token = new mumuki.CsrfToken();
-    var request = token.newRequest({
-      type: 'POST',
-      url: window.location.origin + window.location.pathname + '/solutions' + window.location.search,
-      data: submission
-    });
-
-    return $.ajax(request).then(preRenderResult).done(function (result) {
-      lastSubmission = { content: {solution: submission.solution}, result: result };
-    });
-  }
+/**
+ * @typedef {{
+  *  status: SubmissionStatus,
+  *  class_for_progress_list_item?: string,
+  *  guide_finished_by_solution?: boolean
+  * }} SubmissionResult
+  */
 
+/**
+ * @typedef {object} Solution
+ */
 
-  /**
-   * Pre-renders some html parts of submission UI
-   * */
-  function preRenderResult(result) {
-    result.class_for_progress_list_item = mumuki.renderers.progressListItemClassForStatus(result.status, true)
-    return result;
-  }
+/**
+ * @typedef {{
+ *  "solution[content]"?:string,
+ *  solution?: Solution,
+ *  client_result?: SubmissionClientResult
+ * }} Submission
+ */
 
-  mumuki.load(function () {
-    lastSubmission = {};
-  });
+/**
+ * @typedef {{submission?: Submission, result?: SubmissionResult}} SubmissionAndResult
+ */
 
-  Laboratory.prototype = {
+mumuki.bridge = (() => {
 
+  class Laboratory {
     // ==========
     // Public API
     // ==========
@@ -65,9 +46,9 @@ var mumuki = mumuki || {};
      *
      * @param {object} content the content object
      * */
-    runTests: function(content) {
+    runTests(content) {
       return this._submitSolution({ solution: content });
-    },
+    }
 
     // ===========
     // Private API
@@ -77,18 +58,46 @@ var mumuki = mumuki || {};
      * Sends a solution object
      *
      * @param {Submission} submission the submission object
+     * @returns {JQuery.Promise<SubmissionResult>}
      */
-    _submitSolution: function (submission) {
-      if(lastSubmissionFinishedSuccessfully() && sameAsLastSolution(submission)){
-        return $.Deferred().resolve(lastSubmission.result);
+    _submitSolution(submission) {
+      const lastSubmission = mumuki.SubmissionsStore.getCachedResultFor(mumuki.currentExerciseId, submission);
+      if (lastSubmission) {
+        return $.Deferred().resolve(lastSubmission);
       } else {
-        return sendNewSolution(submission);
+        return this._sendNewSolution(submission).done((result) => {
+          mumuki.SubmissionsStore.setLastSubmission(mumuki.currentExerciseId, {submission, result});
+        });
       }
     }
-  };
 
-  mumuki.bridge = {
-    Laboratory: Laboratory
-  };
+    /**
+     * @param {Submission} submission the submission object
+     * @returns {JQuery.Promise<SubmissionResult>}
+     */
+    _sendNewSolution(submission){
+      var token = new mumuki.CsrfToken();
+      var request = token.newRequest({
+        type: 'POST',
+        url: window.location.origin + window.location.pathname + '/solutions' + window.location.search,
+        data: submission
+      });
+      return $.ajax(request).then((result) => this._preRenderResult(result));
+    }
+
+    /**
+     * Pre-renders some html parts of submission UI, adding them to the given result
+     *
+     * @param {SubmissionResult} result
+     * @returns {SubmissionResult}
+     */
+    _preRenderResult(result) {
+      result.class_for_progress_list_item = mumuki.renderers.progressListItemClassForStatus(result.status, true)
+      return result;
+    }
+  }
 
-}(mumuki));
+  return {
+    Laboratory
+  };
+})();
diff --git a/app/assets/javascripts/mumuki_laboratory/application/current-exercise.js b/app/assets/javascripts/mumuki_laboratory/application/current-exercise.js
new file mode 100644
index 000000000..6f8837e20
--- /dev/null
+++ b/app/assets/javascripts/mumuki_laboratory/application/current-exercise.js
@@ -0,0 +1,13 @@
+/** @type {number} */
+mumuki.currentExerciseId = null;
+(() => {
+  mumuki.load(() => {
+    // Set global currentExerciseId
+    const $muExerciseId = $('#mu-exercise-id');
+    if ($muExerciseId) {
+      mumuki.currentExerciseId = Number($muExerciseId.val());
+    } else {
+      mumuki.currentExerciseId = null;
+    }
+  })
+})();
diff --git a/app/assets/javascripts/mumuki_laboratory/application/results-renderer.js b/app/assets/javascripts/mumuki_laboratory/application/results-renderer.js
index 90ff77ba2..bb1b3d7cb 100644
--- a/app/assets/javascripts/mumuki_laboratory/application/results-renderer.js
+++ b/app/assets/javascripts/mumuki_laboratory/application/results-renderer.js
@@ -6,7 +6,7 @@
   // ==========================
 
   /**
-   * @param {string} status
+   * @param {SubmissionStatus} status
    * @returns {string}
    */
   function iconForStatus(status) {
@@ -20,8 +20,7 @@
   }
 
   /**
-   *
-   * @param {string} status
+   * @param {SubmissionStatus} status
    * @returns {string}
    */
   function classForStatus(status) {
@@ -36,7 +35,7 @@
 
 
   /**
-   * @param {string} status
+   * @param {SubmissionStatus} status
    * @param {boolean} [active]
    * @returns {string}
    */
diff --git a/app/assets/javascripts/mumuki_laboratory/application/submission.js b/app/assets/javascripts/mumuki_laboratory/application/submission.js
index fc6b020aa..81357e25d 100644
--- a/app/assets/javascripts/mumuki_laboratory/application/submission.js
+++ b/app/assets/javascripts/mumuki_laboratory/application/submission.js
@@ -82,6 +82,8 @@ var mumuki = mumuki || {};
    *
    * This method will use CustomEditor's sources if availble, or
    * standard editor's content sources otherwise
+   *
+   * @returns {Submission}
    */
   function getContent() {
     let content = {};
@@ -97,6 +99,7 @@ var mumuki = mumuki || {};
       content[it.name] = it.value;
     });
 
+    // @ts-ignore
     return content;
   }
 
diff --git a/app/assets/javascripts/mumuki_laboratory/application/submissions-store.js b/app/assets/javascripts/mumuki_laboratory/application/submissions-store.js
new file mode 100644
index 000000000..f1ed2d703
--- /dev/null
+++ b/app/assets/javascripts/mumuki_laboratory/application/submissions-store.js
@@ -0,0 +1,85 @@
+mumuki.SubmissionsStore = (() => {
+  const SubmissionsStore = new class {
+    /**
+     * @param {number} exerciseId
+     * @returns {SubmissionStatus}
+     */
+    getLastSubmissionStatus(exerciseId) {
+      const submission = this.getLastSubmission(exerciseId);
+      return submission ? submission.result.status : 'pending';
+    }
+
+    /**
+     * @param {number} exerciseId
+     * @returns {SubmissionAndResult}
+     */
+    getLastSubmission(exerciseId) {
+      const submissionAndResult = window.localStorage.getItem(this._keyFor(exerciseId));
+      if (!submissionAndResult) return null;
+      return JSON.parse(submissionAndResult);
+    }
+
+    /**
+     * @param {number} exerciseId
+     * @param {SubmissionAndResult} submissionAndResult
+     */
+    setLastSubmission(exerciseId, submissionAndResult) {
+      window.localStorage.setItem(this._keyFor(exerciseId), this._asString(submissionAndResult));
+    }
+
+    /**
+     * Retrieves the last cached, non-aborted result for the given submission
+     *
+     * @param {number} exerciseId
+     * @param {Submission} submission
+     * @returns {SubmissionResult} the cached result for this submission
+     */
+    getCachedResultFor(exerciseId, submission) {
+      const lastSubmission = this.getLastSubmission(exerciseId);
+      if (!lastSubmission
+          || lastSubmission.result.status === 'aborted'
+          || !this.submissionSolutionEquals(lastSubmission.submission, submission)) {
+        return null;
+      }
+      return lastSubmission.result;
+    }
+
+     /**
+     * Extract the submission's solution content
+     *
+     * @param {Submission} submission
+     * @returns {string}
+     */
+    submissionSolutionContent(submission) {
+      if (submission.solution) {
+        return submission.solution.content;
+      } else {
+        return submission['solution[content]'];
+      }
+    }
+
+    /**
+     * Compares two solutions to determine if they are equivalent
+     * from the point of view of the code evaluation
+     *
+     * @param {Submission} one
+     * @param {Submission} other
+     * @returns {boolean}
+     */
+    submissionSolutionEquals(one, other) {
+      return this.submissionSolutionContent(one) === this.submissionSolutionContent(other);
+    }
+
+    // private API
+
+    _asString(object) {
+      return JSON.stringify(object);
+    }
+
+    _keyFor(exerciseId) {
+      return `/exercise/${exerciseId}/submission`;
+    }
+  };
+
+  return SubmissionsStore;
+})();
diff --git a/app/views/exercises/show.html.erb b/app/views/exercises/show.html.erb
index 742b76cbf..782a6f5e9 100644
--- a/app/views/exercises/show.html.erb
+++ b/app/views/exercises/show.html.erb
@@ -45,6 +45,7 @@
 <%= render_exercise_input_layout(@exercise) %>
 
 <%= hidden_field_tag default_content_tag_id(@exercise), @default_content %>
+<%= hidden_field_tag "mu-exercise-id", @exercise.id %>
 
 <div style="display: none" id="processing-template">
   <div class="bs-callout bs-callout-info">
diff --git a/app/views/layouts/_progress_bar.html.erb b/app/views/layouts/_progress_bar.html.erb
index 12f9a00eb..3e499cf4c 100644
--- a/app/views/layouts/_progress_bar.html.erb
+++ b/app/views/layouts/_progress_bar.html.erb
@@ -1,6 +1,12 @@
 <div class="progress-list-flex">
   <% guide.exercises.each do |e| %>
-    <a <%= turbolinks_enable_for e %> href="<%= exercise_path(e)%>" aria-label="<%= e.navigable_name %>" title="<%= e.navigable_name %>" class="<%= class_for_progress_list_item(e, e == actual)%>">
+    <a
+      <%= turbolinks_enable_for e %>
+      href="<%= exercise_path(e)%>"
+      aria-label="<%= e.navigable_name %>"
+      title="<%= e.navigable_name %>"
+      data-mu-exercise-id="<%= e.id %>"
+      class="<%= class_for_progress_list_item(e, e == actual)%>">
     </a>
   <% end %>
 </div>
diff --git a/jsconfig.json b/jsconfig.json
index c056cbde1..2eed40500 100644
--- a/jsconfig.json
+++ b/jsconfig.json
@@ -1,6 +1,6 @@
 {
   "compilerOptions": {
-    "module": "commonjs",
+    "module": "none",
     "target": "es6",
     "checkJs": true,
     "allowSyntheticDefaultImports": true