diff --git a/Plan/bukkit/src/main/java/com/djrapitops/plan/system/tasks/BukkitTaskSystem.java b/Plan/bukkit/src/main/java/com/djrapitops/plan/system/tasks/BukkitTaskSystem.java
index f31fa8914..28cfe0396 100644
--- a/Plan/bukkit/src/main/java/com/djrapitops/plan/system/tasks/BukkitTaskSystem.java
+++ b/Plan/bukkit/src/main/java/com/djrapitops/plan/system/tasks/BukkitTaskSystem.java
@@ -31,6 +31,7 @@ import com.djrapitops.plugin.task.RunnableFactory;
 import org.bukkit.Bukkit;
 
 import javax.inject.Inject;
+import java.util.Optional;
 import java.util.concurrent.TimeUnit;
 
 /**
@@ -88,6 +89,6 @@ public class BukkitTaskSystem extends ServerTaskSystem {
     @Override
     public void disable() {
         super.disable();
-        Bukkit.getScheduler().cancelTasks(plugin);
+        Optional.ofNullable(Bukkit.getScheduler()).ifPresent(scheduler -> scheduler.cancelTasks(plugin));
     }
 }
diff --git a/Plan/common/src/main/java/com/djrapitops/plan/utilities/file/export/HtmlExport.java b/Plan/common/src/main/java/com/djrapitops/plan/utilities/file/export/HtmlExport.java
index 506a25217..8b1957c51 100644
--- a/Plan/common/src/main/java/com/djrapitops/plan/utilities/file/export/HtmlExport.java
+++ b/Plan/common/src/main/java/com/djrapitops/plan/utilities/file/export/HtmlExport.java
@@ -174,6 +174,7 @@ public class HtmlExport extends SpecificExport {
 
     private void exportJs() {
         String[] resources = new String[]{
+                "web/js/demo.js",
                 "web/js/admin.js",
                 "web/js/helpers.js",
                 "web/js/script.js",
diff --git a/Plan/common/src/main/java/com/djrapitops/plan/utilities/html/pages/DebugPage.java b/Plan/common/src/main/java/com/djrapitops/plan/utilities/html/pages/DebugPage.java
index c9a4efd9e..910711ea8 100644
--- a/Plan/common/src/main/java/com/djrapitops/plan/utilities/html/pages/DebugPage.java
+++ b/Plan/common/src/main/java/com/djrapitops/plan/utilities/html/pages/DebugPage.java
@@ -60,7 +60,7 @@ public class DebugPage implements Page {
     private final ConnectionSystem connectionSystem;
     private final CombineDebugLogger debugLogger;
     private final Timings timings;
-    private final DefaultErrorHandler errorHandler;
+    private final ErrorHandler errorHandler;
 
     private final Formatter<DateHolder> secondFormatter;
     private final Formatter<Long> yearFormatter;
@@ -79,7 +79,7 @@ public class DebugPage implements Page {
         this.connectionSystem = connectionSystem;
         this.debugLogger = (CombineDebugLogger) debugLogger;
         this.timings = timings;
-        this.errorHandler = (DefaultErrorHandler) errorHandler;
+        this.errorHandler = errorHandler;
 
         this.secondFormatter = formatters.second();
         this.yearFormatter = formatters.yearLong();
@@ -268,6 +268,16 @@ public class DebugPage implements Page {
     private void appendLoggedErrors(StringBuilder content) {
         content.append("<pre>### Logged Errors<br>");
 
+        if (errorHandler instanceof DefaultErrorHandler) {
+            appendErrorLines(content, (DefaultErrorHandler) errorHandler);
+        } else {
+            content.append("Using incompatible ErrorHandler");
+        }
+
+        content.append("</pre>");
+    }
+
+    private void appendErrorLines(StringBuilder content, DefaultErrorHandler errorHandler) {
         List<String> lines = errorHandler.getErrorHandler(FolderTimeStampErrorFileLogger.class)
                 .flatMap(FolderTimeStampFileLogger::getCurrentFile)
                 .map(file -> {
@@ -300,7 +310,6 @@ public class DebugPage implements Page {
         } else {
             content.append("**No Errors logged.**<br>");
         }
-        content.append("</pre>");
     }
 
     private void appendDebugLog(StringBuilder content) {
diff --git a/Plan/common/src/main/resources/web/player.html b/Plan/common/src/main/resources/web/player.html
index ff432cca5..3c030df11 100644
--- a/Plan/common/src/main/resources/web/player.html
+++ b/Plan/common/src/main/resources/web/player.html
@@ -32,6 +32,9 @@
     <!-- AdminBSB Themes. You can choose a theme from css/themes instead of get all themes -->
     <link href="../css/themes/all-themes.css" rel="stylesheet"/>
 
+    <!-- Jquery Core Js -->
+    <script src="../plugins/jquery/jquery.min.js"></script>
+
     <!-- Font Awesome -->
     <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
     <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.2.0/css/all.css" integrity="sha384-hWVjflwFxL6sNzntih27bfxkr27PmbbK/iSvJ+a4+0owXq79v+lsFkW54bOGbiDQ" crossorigin="anonymous">
@@ -795,9 +798,6 @@
     </div>
 </section>
 
-<!-- Jquery Core Js -->
-<script src="../plugins/jquery/jquery.min.js"></script>
-
 <!-- Bootstrap Core Js -->
 <script src="../plugins/bootstrap/js/bootstrap.js"></script>
 
diff --git a/Plan/common/src/test/java/utilities/mocks/Mocker.java b/Plan/common/src/test/java/utilities/mocks/Mocker.java
index 983f37a89..6b93bc509 100644
--- a/Plan/common/src/test/java/utilities/mocks/Mocker.java
+++ b/Plan/common/src/test/java/utilities/mocks/Mocker.java
@@ -5,10 +5,12 @@
 package utilities.mocks;
 
 import com.djrapitops.plan.PlanPlugin;
+import org.mockito.Mockito;
 
 import java.io.*;
 
 import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.when;
 
 /**
  * Abstract Mocker for methods that can be used for both Bungee and Bukkit.
@@ -58,14 +60,61 @@ abstract class Mocker {
     }
 
     void withPluginFiles() throws Exception {
-        withPluginFile("bungeeconfig.yml");
-        withPluginFile("config.yml");
-        withPluginFile("web/server.html");
-        withPluginFile("web/player.html");
-        withPluginFile("web/network.html");
-        withPluginFile("web/error.html");
-        withPluginFile("themes/theme.yml");
-        withPluginFile("DefaultServerInfoFile.yml");
+        when(planMock.getResource(Mockito.anyString())).thenCallRealMethod();
+        for (String fileName : new String[]{
+                "bungeeconfig.yml",
+                "config.yml",
+                "DefaultServerInfoFile.yml",
+                "themes/theme.yml",
+
+                "web/server.html",
+                "web/player.html",
+                "web/network.html",
+                "web/error.html",
+
+                "web/css/main.css",
+                "web/css/materialize.css",
+                "web/css/style.css",
+                "web/css/themes/all-themes.css",
+
+                "web/js/demo.js",
+                "web/js/admin.js",
+                "web/js/helpers.js",
+                "web/js/script.js",
+                "web/js/charts/activityPie.js",
+                "web/js/charts/lineGraph.js",
+                "web/js/charts/horizontalBarGraph.js",
+                "web/js/charts/stackGraph.js",
+                "web/js/charts/performanceGraph.js",
+                "web/js/charts/playerGraph.js",
+                "web/js/charts/playerGraphNoNav.js",
+                "web/js/charts/resourceGraph.js",
+                "web/js/charts/diskGraph.js",
+                "web/js/charts/tpsGraph.js",
+                "web/js/charts/worldGraph.js",
+                "web/js/charts/worldMap.js",
+                "web/js/charts/punchCard.js",
+                "web/js/charts/serverPie.js",
+                "web/js/charts/worldPie.js",
+                "web/js/charts/healthGauge.js",
+                "web/js/charts/sessionCalendar.js",
+                "web/js/charts/onlineActivityCalendar.js",
+
+                "web/plugins/bootstrap/css/bootstrap.css",
+                "web/plugins/node-waves/waves.css",
+                "web/plugins/node-waves/waves.js",
+                "web/plugins/animate-css/animate.css",
+                "web/plugins/jquery-slimscroll/jquery.slimscroll.js",
+                "web/plugins/jquery/jquery.min.js",
+                "web/plugins/bootstrap/js/bootstrap.js",
+                "web/plugins/jquery-datatable/skin/bootstrap/js/dataTables.bootstrap.js",
+                "web/plugins/jquery-datatable/jquery.dataTables.js",
+                "web/plugins/fullcalendar/fullcalendar.min.js",
+                "web/plugins/fullcalendar/fullcalendar.min.css",
+                "web/plugins/momentjs/moment.js"
+        }) {
+            withPluginFile(fileName);
+        }
     }
 
 }
diff --git a/Plan/plugin/src/test/java/com/djrapitops/plan/system/webserver/JSErrorRegressionTest.java b/Plan/plugin/src/test/java/com/djrapitops/plan/system/webserver/JSErrorRegressionTest.java
new file mode 100644
index 000000000..e46b1ea2e
--- /dev/null
+++ b/Plan/plugin/src/test/java/com/djrapitops/plan/system/webserver/JSErrorRegressionTest.java
@@ -0,0 +1,128 @@
+package com.djrapitops.plan.system.webserver;
+
+import com.djrapitops.plan.DaggerPlanBukkitComponent;
+import com.djrapitops.plan.PlanBukkitComponent;
+import com.djrapitops.plan.data.container.Session;
+import com.djrapitops.plan.system.PlanSystem;
+import com.djrapitops.plan.system.database.DBSystem;
+import com.djrapitops.plan.system.database.databases.operation.SaveOperations;
+import com.djrapitops.plan.system.settings.Settings;
+import com.djrapitops.plan.system.settings.config.PlanConfig;
+import com.djrapitops.plan.system.webserver.cache.PageId;
+import com.djrapitops.plan.system.webserver.cache.ResponseCache;
+import com.jayway.awaitility.Awaitility;
+import org.junit.*;
+import org.junit.rules.TemporaryFolder;
+import org.junit.runner.RunWith;
+import org.mockito.junit.MockitoJUnitRunner;
+import org.openqa.selenium.WebDriver;
+import rules.SeleniumDriver;
+import utilities.TestConstants;
+import utilities.mocks.PlanBukkitMocker;
+
+import java.util.UUID;
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.Assert.assertFalse;
+
+/**
+ * This test class is for catching any JavaScript errors.
+ * <p>
+ * Errors may have been caused by:
+ * - Missing placeholders {@code ${placeholder}} inside {@code <script>} tags.
+ * - Automatic formatting of plugin javascript (See https://github.com/Rsl1122/Plan-PlayerAnalytics/issues/820)
+ * - Missing file definition in {@link utilities.mocks.Mocker}
+ */
+@RunWith(MockitoJUnitRunner.Silent.class)
+public class JSErrorRegressionTest {
+
+    @ClassRule
+    public static TemporaryFolder temporaryFolder = new TemporaryFolder();
+    @ClassRule
+    public static SeleniumDriver seleniumDriver = new SeleniumDriver();
+
+    private static PlanSystem bukkitSystem;
+
+    @BeforeClass
+    public static void setUpClass() throws Exception {
+        PlanBukkitMocker mocker = PlanBukkitMocker.setUp()
+                .withDataFolder(temporaryFolder.getRoot())
+                .withPluginDescription()
+                .withResourceFetchingFromJar()
+                .withServer();
+        PlanBukkitComponent component = DaggerPlanBukkitComponent.builder().plan(mocker.getPlanMock()).build();
+
+        bukkitSystem = component.system();
+
+        PlanConfig config = bukkitSystem.getConfigSystem().getConfig();
+        config.set(Settings.WEBSERVER_PORT, 9005);
+
+        bukkitSystem.enable();
+        savePlayerData();
+    }
+
+    private static void savePlayerData() {
+        DBSystem dbSystem = bukkitSystem.getDatabaseSystem();
+        SaveOperations save = dbSystem.getDatabase().save();
+        UUID uuid = TestConstants.PLAYER_ONE_UUID;
+        save.registerNewUser(uuid, 1000L, "TestPlayer");
+        Session session = new Session(uuid, TestConstants.SERVER_UUID, 1000L, "world", "SURVIVAL");
+        session.endSession(11000L);
+        save.session(uuid, session);
+    }
+
+    @After
+    public void tearDownTest() {
+        seleniumDriver.newTab();
+    }
+
+    @AfterClass
+    public static void tearDownClass() {
+        if (bukkitSystem != null) {
+            bukkitSystem.disable();
+        }
+    }
+
+    @Test
+    public void playerPageDoesNotHaveJavascriptErrors() {
+        System.out.println("Testing Player Page");
+        WebDriver driver = seleniumDriver.getDriver();
+        driver.get("http://localhost:9005/player/TestPlayer");
+        assertFalse(driver.getPageSource(), driver.getPageSource().contains("500 Internal Error occurred"));
+    }
+
+    @Test
+    public void serverPageDoesNotHaveJavascriptErrors() {
+        System.out.println("Testing Server Page");
+        WebDriver driver = seleniumDriver.getDriver();
+        // Open the page that has refreshing info
+        driver.get("http://localhost:9005/server");
+        assertFalse(driver.getPageSource(), driver.getPageSource().contains("500 Internal Error occurred"));
+
+        // Wait until Plan caches analysis results
+        Awaitility.await()
+                .atMost(5, TimeUnit.SECONDS)
+                .until(() -> ResponseCache.isCached(PageId.SERVER.of(TestConstants.SERVER_UUID)));
+
+        // Open the page with analysis stuff
+        seleniumDriver.newTab();
+        driver.get("http://localhost:9005/server");
+        assertFalse(driver.getPageSource(), driver.getPageSource().contains("500 Internal Error occurred"));
+    }
+
+    @Test
+    public void playersPageDoesNotHaveJavascriptErrors() {
+        System.out.println("Testing Players Page");
+        WebDriver driver = seleniumDriver.getDriver();
+        driver.get("http://localhost:9005/players");
+        assertFalse(driver.getPageSource(), driver.getPageSource().contains("500 Internal Error occurred"));
+    }
+
+    @Test
+    public void debugPageDoesNotHaveJavascriptErrors() {
+        System.out.println("Testing Debug Page");
+        WebDriver driver = seleniumDriver.getDriver();
+        driver.get("http://localhost:9005/debug");
+        assertFalse(driver.getPageSource(), driver.getPageSource().contains("500 Internal Error occurred"));
+    }
+}
\ No newline at end of file
diff --git a/Plan/plugin/src/test/java/rules/SeleniumDriver.java b/Plan/plugin/src/test/java/rules/SeleniumDriver.java
new file mode 100644
index 000000000..c7673018f
--- /dev/null
+++ b/Plan/plugin/src/test/java/rules/SeleniumDriver.java
@@ -0,0 +1,70 @@
+/*
+ *  This file is part of Player Analytics (Plan).
+ *
+ *  Plan is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Lesser General Public License v3 as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  Plan is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public License
+ *  along with Plan. If not, see <https://www.gnu.org/licenses/>.
+ */
+package rules;
+
+import org.apache.commons.lang3.SystemUtils;
+import org.junit.Assume;
+import org.junit.rules.ExternalResource;
+import org.openqa.selenium.By;
+import org.openqa.selenium.Keys;
+import org.openqa.selenium.WebDriver;
+import org.openqa.selenium.WebElement;
+import org.openqa.selenium.chrome.ChromeDriver;
+
+import java.io.File;
+import java.util.ArrayList;
+
+public class SeleniumDriver extends ExternalResource {
+
+    private WebDriver driver;
+
+    @Override
+    protected void before() {
+        String driverLocation = getChromeDriverLocation();
+        Assume.assumeNotNull("rules.SeleniumDriver: Chrome driver location not specified for this OS type", driverLocation);
+        Assume.assumeTrue("rules.SeleniumDriver: Chrome driver not found at " + driverLocation, new File(driverLocation).exists());
+
+        System.setProperty("webdriver.chrome.driver", driverLocation);
+        driver = new ChromeDriver();
+    }
+
+    private String getChromeDriverLocation() {
+        if (SystemUtils.IS_OS_LINUX) {
+            return "/usr/local/share/chromedriver";
+        } else if (SystemUtils.IS_OS_WINDOWS) {
+            return "C:\\chromedriver.exe";
+        }
+        return null;
+    }
+
+    public void newTab() {
+        WebElement body = driver.findElement(By.tagName("body"));
+        body.sendKeys(Keys.CONTROL + "t");
+        driver.switchTo().window(new ArrayList<>(driver.getWindowHandles()).get(0));
+    }
+
+    public WebDriver getDriver() {
+        return driver;
+    }
+
+    @Override
+    protected void after() {
+        if (driver != null) {
+            driver.quit();
+        }
+    }
+}
diff --git a/Plan/pom.xml b/Plan/pom.xml
index e2783191b..1c0402a72 100644
--- a/Plan/pom.xml
+++ b/Plan/pom.xml
@@ -59,7 +59,6 @@
             <groupId>org.mockito</groupId>
             <artifactId>mockito-core</artifactId>
             <version>2.23.4</version>
-            <type>jar</type>
             <scope>test</scope>
         </dependency>
         <dependency>
@@ -80,6 +79,19 @@
             <version>1.3</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.seleniumhq.selenium</groupId>
+            <artifactId>selenium-java</artifactId>
+            <version>3.14.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.jayway.awaitility</groupId>
+            <artifactId>awaitility</artifactId>
+            <version>1.7.0</version>
+            <scope>test</scope>
+        </dependency>
+
 
         <!-- Dependency injection is used across the whole project.-->
         <dependency>