diff --git a/templates/custom-functions/Code.gs b/templates/custom-functions/Code.gs
index 97b1325ff..48c1b4d4b 100644
--- a/templates/custom-functions/Code.gs
+++ b/templates/custom-functions/Code.gs
@@ -22,8 +22,8 @@
  * A function that takes a single input value and returns a single value.
  * Returns a simple concatenation of Strings.
  *
- * @param {String} name A name to greet.
- * @return {String} A greeting.
+ * @param {string} name A name to greet.
+ * @return {string} A greeting.
  * @customfunction
  */
 function SAY_HELLO(name) {
@@ -35,8 +35,8 @@ function SAY_HELLO(name) {
  * range of cells.
  * Returns a range with all the input values incremented by one.
  *
- * @param {Array} input The range of numbers to increment.
- * @return {Array} The incremented values.
+ * @param {any} input The range of numbers to increment.
+ * @return {any} The incremented values.
  * @customfunction
  */
 function INCREMENT(input) {
@@ -55,8 +55,8 @@ function INCREMENT(input) {
  * Returns the sum the corner values in the range; for a single cell,
  * this is equal to (4 * the cell value).
  *
- * @param {Array} input The Range of numbers to sum the corners of.
- * @return {Number} The calculated sum.
+ * @param {number | number[][]} input The Range of numbers to sum the corners of.
+ * @return {number} The calculated sum.
  * @customfunction
  */
 function CORNER_SUM(input) {
@@ -65,8 +65,8 @@ function CORNER_SUM(input) {
     return CORNER_SUM([[input]]); // eslint-disable-line new-cap
   }
   // Range processing here.
-  var maxRowIndex = input.length - 1;
-  var maxColIndex = input[0].length - 1;
+  const maxRowIndex = input.length - 1;
+  const maxColIndex = input[0].length - 1;
   return input[0][0] + input[0][maxColIndex] +
       input[maxRowIndex][0] + input[maxRowIndex][maxColIndex];
 }
@@ -76,20 +76,21 @@ function CORNER_SUM(input) {
  * Returns a range consisting of the first 10 powers and roots of that
  * number (with column headers).
  *
- * @param {Number} input The number to calculate from.
- * @return {Array} The first ten powers and roots of that number,
- *     with associated labels.
+ * @param {number} input The number to calculate from.
+ * @return {Array<Array<string|number>>} The first ten powers and roots of that
+ *     number, with associated labels.
  * @customfunction
  */
 function POWERS_AND_ROOTS(input) {
-  if (input instanceof Array) {
-    throw new Error('Invalid: Range input not permitted');
+  if (typeof input !== 'number') {
+    throw new Error('Invalid: A single number is required.');
   }
   // Value processing and range generation here.
-  var headers = ['x', input + '^x', input + '^(1/x)'];
-  var result = [headers];
-  for (var i = 1; i <= 10; i++) {
-    result.push([i, Math.pow(input, i), Math.pow(input, 1/i)]);
+  const headers = ['x', input.toString() + '^x', input.toString() + '^(1/x)'];
+  /** @type {Array<Array<string|number>>} */
+  const result = [headers];
+  for (let i = 1; i <= 10; i++) {
+    result.push([i, Math.pow(input, i), Math.pow(input, 1 / i)]);
   }
   return result;
 }
@@ -99,7 +100,7 @@ function POWERS_AND_ROOTS(input) {
  * Returns the day of the year represented by the provided date.
  *
  * @param {Date} date A Date to examine.
- * @return {Number} The day of year for that date.
+ * @return {number} The day of year for that date.
  * @customfunction
  */
 function GET_DAY_OF_YEAR(date) {
@@ -107,9 +108,9 @@ function GET_DAY_OF_YEAR(date) {
     throw new Error('Invalid: Date input required');
   }
   // Date processing here.
-  var firstOfYear = new Date(date.getFullYear(), 0, 0);
-  var diff = date - firstOfYear;
-  var oneDay = 1000 * 60 * 60 * 24;
+  const firstOfYear = new Date(date.getFullYear(), 0, 0);
+  const diff = date.getTime() - firstOfYear.getTime();
+  const oneDay = 1000 * 60 * 60 * 24;
   return Math.floor(diff / oneDay);
 }
 
@@ -118,7 +119,7 @@ function GET_DAY_OF_YEAR(date) {
  * Returns the number of seconds measured by that duration.
  *
  * @param {Date} duration A duration to convert.
- * @return {Number} Number of seconds in that duration.
+ * @return {number} Number of seconds in that duration.
  * @customfunction
  */
 function CONVERT_DURATION_TO_SECONDS(duration) {
diff --git a/templates/docs-addon/Code.gs b/templates/docs-addon/Code.gs
index 1c4ad0c29..48a14e3b7 100644
--- a/templates/docs-addon/Code.gs
+++ b/templates/docs-addon/Code.gs
@@ -24,7 +24,7 @@ var SIDEBAR_TITLE = 'Example Sidebar';
 /**
  * Adds a custom menu with items to show the sidebar and dialog.
  *
- * @param {Object} e The event parameter for a simple onOpen trigger.
+ * @param {any} e The event parameter for a simple onOpen trigger.
  */
 function onOpen(e) {
   DocumentApp.getUi()
@@ -38,7 +38,7 @@ function onOpen(e) {
  * Runs when the add-on is installed; calls onOpen() to ensure menu creation and
  * any other initializion work is done immediately.
  *
- * @param {Object} e The event parameter for a simple onInstall trigger.
+ * @param {any} e The event parameter for a simple onInstall trigger.
  */
 function onInstall(e) {
   onOpen(e);
@@ -70,7 +70,7 @@ function showDialog() {
 /**
  * Returns the existing footer text (if any).
  *
- * @return {String} existing document footer text (as a plain string).
+ * @return {string} existing document footer text (as a plain string).
  */
 function getFooterText() {
   // Retrieve and return the information requested by the sidebar.
@@ -80,7 +80,7 @@ function getFooterText() {
 /**
  * Replaces the current document footer with the given text.
  *
- * @param {String} footerText text collected from the client-side
+ * @param {string} footerText text collected from the client-side
  *     sidebar.
  */
 function setFooterText(footerText) {
@@ -91,7 +91,7 @@ function setFooterText(footerText) {
 /**
  * Returns the document title.
  *
- * @return {String} the current document title.
+ * @return {string} the current document title.
  */
 function getDocTitle() {
   // Retrieve and return the information requested by the dialog.
@@ -101,7 +101,7 @@ function getDocTitle() {
 /**
  * Changes the document title.
  *
- * @param {String} title the new title to use for the document.
+ * @param {string} title the new title to use for the document.
  */
 function setDocTitle(title) {
   // Use data collected from dialog to manipulate the document.
diff --git a/templates/forms-addon/Code.gs b/templates/forms-addon/Code.gs
index 295256f4b..08b5ec0bd 100644
--- a/templates/forms-addon/Code.gs
+++ b/templates/forms-addon/Code.gs
@@ -24,7 +24,7 @@ var SIDEBAR_TITLE = 'Example Sidebar';
 /**
  * Adds a custom menu with items to show the sidebar and dialog.
  *
- * @param {Object} e The event parameter for a simple onOpen trigger.
+ * @param {any} e The event parameter for a simple onOpen trigger.
  */
 function onOpen(e) {
   FormApp.getUi()
@@ -38,7 +38,7 @@ function onOpen(e) {
  * Runs when the add-on is installed; calls onOpen() to ensure menu creation and
  * any other initializion work is done immediately.
  *
- * @param {Object} e The event parameter for a simple onInstall trigger.
+ * @param {any} e The event parameter for a simple onInstall trigger.
  */
 function onInstall(e) {
   onOpen(e);
@@ -67,10 +67,17 @@ function showDialog() {
   FormApp.getUi().showModalDialog(ui, DIALOG_TITLE);
 }
 
+/**
+ * @typedef {{
+ *   type: string,
+ *   name: string,
+ * }} ItemData
+ */
+
 /**
  * Appends a new form item to the current form.
  *
- * @param {Object} itemData a collection of String data used to
+ * @param {ItemData} itemData a collection of String data used to
  *     determine the exact form item created.
  */
 function addFormItem(itemData) {
@@ -93,7 +100,7 @@ function addFormItem(itemData) {
  * Queries the form DocumentProperties to determine whether the formResponse
  * trigger is enabled or not.
  *
- * @return {Boolean} True if the form submit trigger is enabled; false
+ * @return {boolean} True if the form submit trigger is enabled; false
  *     otherwise.
  */
 function getTriggerState() {
@@ -105,7 +112,7 @@ function getTriggerState() {
 /**
  * Turns the form submit trigger on or off based on the given argument.
  *
- * @param {Boolean} enableTrigger whether to turn on the form submit
+ * @param {boolean} enableTrigger whether to turn on the form submit
  *     trigger or not
  */
 function adjustFormSubmitTrigger(enableTrigger) {
@@ -136,12 +143,18 @@ function adjustFormSubmitTrigger(enableTrigger) {
   }
 }
 
+/**
+ * @typedef {{
+ *  response: GoogleAppsScript.Forms.FormResponse
+ * }} FormSubmitEvent
+ */
+
 /**
  * Responds to form submit events if a form summit trigger is enabled.
  * Collects some form information and sends it as an email to the form creator.
  *
- * @param {Object} e The event parameter created by a form
- *      submission; see
+ * @param {FormSubmitEvent} e The event parameter
+ *     created by a form submission.
  *      https://developers.google.com/apps-script/understanding_events
  */
 function respondToFormSubmit(e) {
diff --git a/templates/sheets-addon/Code.gs b/templates/sheets-addon/Code.gs
index 2c862bf51..9a956b453 100644
--- a/templates/sheets-addon/Code.gs
+++ b/templates/sheets-addon/Code.gs
@@ -24,7 +24,7 @@ var SIDEBAR_TITLE = 'Example Sidebar';
 /**
  * Adds a custom menu with items to show the sidebar and dialog.
  *
- * @param {Object} e The event parameter for a simple onOpen trigger.
+ * @param {any} e The event parameter for a simple onOpen trigger.
  */
 function onOpen(e) {
   SpreadsheetApp.getUi()
@@ -38,7 +38,7 @@ function onOpen(e) {
  * Runs when the add-on is installed; calls onOpen() to ensure menu creation and
  * any other initializion work is done immediately.
  *
- * @param {Object} e The event parameter for a simple onInstall trigger.
+ * @param {any} e The event parameter for a simple onInstall trigger.
  */
 function onInstall(e) {
   onOpen(e);
@@ -70,7 +70,7 @@ function showDialog() {
 /**
  * Returns the value in the active cell.
  *
- * @return {String} The value of the active cell.
+ * @return {string} The value of the active cell.
  */
 function getActiveValue() {
   // Retrieve and return the information requested by the sidebar.
@@ -81,7 +81,7 @@ function getActiveValue() {
 /**
  * Replaces the active cell value with the given value.
  *
- * @param {Number} value A reference number to replace with.
+ * @param {number} value A reference number to replace with.
  */
 function setActiveValue(value) {
   // Use data collected from sidebar to manipulate the sheet.
@@ -93,7 +93,7 @@ function setActiveValue(value) {
  * Executes the specified action (create a new sheet, copy the active sheet, or
  * clear the current sheet).
  *
- * @param {String} action An identifier for the action to take.
+ * @param {string} action An identifier for the action to take.
  */
 function modifySheets(action) {
   // Use data collected from dialog to manipulate the spreadsheet.
diff --git a/templates/sheets-import/APICode.gs b/templates/sheets-import/APICode.gs
index 5bbdb7d9a..0f15bff7b 100644
--- a/templates/sheets-import/APICode.gs
+++ b/templates/sheets-import/APICode.gs
@@ -1,3 +1,4 @@
+// @ts-nocheck
 /**
  * Copyright Google LLC
  *
@@ -14,10 +15,17 @@
  * limitations under the License.
  */
 
+/**
+ * @typedef {{
+ *   id: string,
+ *   label: string,
+ * }} ColumnOption
+ */
+
 /**
  * Return an array of potential columns (identifiers to locate them in
  * the data response object and the labels to use as column headers).
- * @return {Array} list of potential columns.
+ * @return {ColumnOption[]} list of potential columns.
  */
 function getColumnOptions() {
   var columns = [];
@@ -37,15 +45,15 @@ function getColumnOptions() {
  * Return a page of results from the data source as a 2D array of
  * values (with columns corresponding to the columns specified). Return
  * null if no data exists for the specified pageNumber.
- * @param {Array} columns an array of Strings specifying the column ids
+ * @param {string[]} columns an array of Strings specifying the column ids
  *   to include in the output.
- * @param {Number} pageNumber a number indicating what page of data to
+ * @param {number} pageNumber a number indicating what page of data to
  *   retrieve from the data source.
- * @param {Number} pageSize a number indicating the maximum number of
+ * @param {number} pageSize a number indicating the maximum number of
  *   rows to return per call.
- * @param {Object} opt_settings optional object containing any additional
- *   information needed to retrieve data from the data source.
- * @return {object[]|null} Pages of data.
+ * @param {Object<string, string>} opt_settings optional object containing any
+ *   additional information needed to retrieve data from the data source.
+ * @return {Object<string, any>|null} Pages of data.
  */
 function getDataPage(columns, pageNumber, pageSize, opt_settings) {
   var data = null;
diff --git a/templates/sheets-import/Auth.gs b/templates/sheets-import/Auth.gs
index f303e4bb5..ca3c1c3af 100644
--- a/templates/sheets-import/Auth.gs
+++ b/templates/sheets-import/Auth.gs
@@ -1,3 +1,4 @@
+// @ts-nocheck
 /**
  * Copyright 2015 Google Inc. All Rights Reserved.
  *
@@ -14,15 +15,37 @@
  * limitations under the License.
  */
 
+// @ts-nocheck
+var OAuth2 = undefined;
+
+/**
+ * @typedef {{
+ *  setAuthorizationBaseUrl: (url: string) => Service,
+ *  setTokenUrl: (url: string) => Service,
+ *  setClientId: (id: string) => Service,
+ *  setClientSecret: (secret: string) => Service,
+ *  setCallbackFunction: (handler: string) => Service,
+ *  setPropertyStore: (store: GoogleAppsScript.Properties.Properties) => Service,
+ *  getAuthorizationUrl: () => string,
+ *  reset: () => void,
+ *  handleCallback: (request: Object<string, string>) => boolean,
+ *  hasAccess: () => boolean,
+ * }} Service
+ */
+
 /**
  * Return an OAuth service object to handle authorization for a specific
  * data source (such as an API resource). Makes use of the OAuth2 Apps
  * Script library:
  *   https://github.com/googlesamples/apps-script-oauth2
- * @return {Object} a service object associated with the specified
- *   resource.
+ * @return {Service} a service object associated with
+ *   the specified resource.
  */
 function getService() {
+  if (typeof OAuth2 === 'undefined') {
+    throw new Error('OAuth2 library not found. Have you added it?');
+  }
+
   /* TODO: Fill in the following required parameters for your data source. */
   var service = OAuth2.createService('ENTER_SERVICE_NAME_HERE')
       .setAuthorizationBaseUrl('ENTER_BASE_URL_HERE')
@@ -46,32 +69,23 @@ function getService() {
  * completion of the API auth sequence. For additional details, see the
  * OAuth2 Apps Script library:
  *   https://github.com/googlesamples/apps-script-oauth2
- * @param {Object} request results of API auth request.
- * @return {HTML} A auth callback HTML page.
+ * @param {Object<string, string>} request results of API auth request.
+ * @return {GoogleAppsScript.HTML.HtmlOutput} A auth callback HTML page.
  */
 function authCallback(request) {
   var template = HtmlService.createTemplateFromFile('AuthCallbackView');
   template.user = Session.getEffectiveUser().getEmail();
-  template.isAuthorized = false;
-  template.error = null;
-  var title;
-  try {
-    var service = getService();
-    var authorized = service.handleCallback(request);
-    template.isAuthorized = authorized;
-    title = authorized ? 'Access Granted' : 'Access Denied';
-  } catch (e) {
-    template.error = e;
-    title = 'Access Error';
-  }
+  var service = getService();
+  var authorized = service.handleCallback(request);
+  template.isAuthorized = authorized;
+  var title = authorized ? 'Access Granted' : 'Access Denied';
   template.title = title;
-  return template.evaluate()
-      .setTitle(title);
+  return template.evaluate().setTitle(title);
 }
 
 /**
  * Builds and returns the API authorization URL from the service object.
- * @return {String} the API authorization URL.
+ * @return {string} the API authorization URL.
  */
 function getAuthorizationUrl() {
   return getService().getAuthorizationUrl();
diff --git a/templates/sheets-import/Configurations.gs b/templates/sheets-import/Configurations.gs
index 3f40fb100..67e2b75e5 100644
--- a/templates/sheets-import/Configurations.gs
+++ b/templates/sheets-import/Configurations.gs
@@ -1,3 +1,4 @@
+// @ts-nocheck
 /**
  * Copyright 2015 Google Inc. All Rights Reserved.
  *
@@ -14,6 +15,7 @@
  * limitations under the License.
  */
 
+// @ts-nocheck
 var REPORT_SET_KEY = 'Import.ReportSet';
 var SCHEDULE_TRIGGER_ID = 'Import.scheduled.triggerId';
 
@@ -25,11 +27,30 @@ var UPDATE_TYPE = {
   REMOVE: 2
 };
 
+/**
+ * @typedef {{
+ *   reportId: string,
+ *   sheetId: string,
+ *   sheetName: string,
+ *   name: string,
+ *   lastRun: string,
+ *   owner: string,
+ *   scheduled: boolean,
+ *   columns: any[],
+ * }} ReportConfig
+ */
+
+/**
+ * @typedef {{
+ *  [reportId: string]: string
+ * }} Report
+ */
+
 /**
  * Return the report configuration for the report with the given
  * ID; returns an empty Object if no such report name exists.
- * @param {String} reportId a report ID.
- * @return {Object} a report configuration corresponding to that ID,
+ * @param {string} reportId a report ID.
+ * @return {ReportConfig|null} a report configuration corresponding to that ID,
  *   or null if no such report exists.
  */
 function getReportConfig(reportId) {
@@ -41,22 +62,24 @@ function getReportConfig(reportId) {
   // get the current one.
   var ss = SpreadsheetApp.getActiveSpreadsheet();
   var sheet = getSheetById(ss, parseInt(config.sheetId));
-  config.sheetName = !sheet ? null : sheet.getName();
-  return config;
+  config.sheetName = !sheet ? '' : sheet.getName();
+  return /** @type {ReportConfig} */ (config);
 }
 
 /**
  * Given a report configuration, save it.
- * @param {object} config the report configuration.
- * @param {object} the updated report configuration.
- * @return {object} The saved configuration.
+ * @param {ReportConfig} config the report configuration.
+ * @return {ReportConfig} The saved configuration.
  */
 function saveReportConfig(config) {
+  if (typeof _ === 'undefined') {
+    throw new Error('Underscore library not found. Have you added it?');
+  }
   var previous = getReportConfig(config.reportId);
   if (config.reportId === 'new-report') {
     config.reportId = newReportId();
-    config.lastRun = null;
-    config.owner = Session.getEffectiveUser().getEmail();
+    config.lastRun = '';
+    config.owner = Session.getEffectiveUser().getEmail() || '';
   }
   saveObjectToProperties(config.reportId, config);
   updateReportSet(UPDATE_TYPE.ADD, config.reportId, config.name);
@@ -68,7 +91,7 @@ function saveReportConfig(config) {
 
 /**
  * Delete the report specified by the given ID.
- * @param {String} reportId indicates the report to delete.
+ * @param {string} reportId indicates the report to delete.
  */
 function deleteReportConfig(reportId) {
   deleteObjectFromProperties(reportId);
@@ -78,7 +101,7 @@ function deleteReportConfig(reportId) {
 /**
  * Returns true if the current user is allowed to edit the
  * report associated with the given config.
- * @param {Object} config a report configuration.
+ * @param {ReportConfig} config a report configuration.
  * @return {boolean} True if the user can edit the report.
  */
 function canEditReport(config) {
@@ -92,7 +115,7 @@ function canEditReport(config) {
 /**
  * Given a new report configuration, return true if it saving this report would mean the limit on
  * scheduled reports would be exceeded.
- * @param {Object} config a report configuration to be saved.
+ * @param {ReportConfig} config a report configuration to be saved.
  * @return {boolean} If it saving this report would mean the limit on scheduled reports
  * would be exceeded.
  */
@@ -108,46 +131,59 @@ function isOverScheduleLimit(config) {
 /**
  * Return a set of all saved reports (reportIds as keys, report
  * names as values).
- * @return {Object}
+ * @return {Report}
  */
 function getAllReports() {
   var properties = PropertiesService.getDocumentProperties();
-  return JSON.parse(properties.getProperty(REPORT_SET_KEY));
+  var reports = properties.getProperty(REPORT_SET_KEY);
+  if (reports) {
+    return JSON.parse(reports);
+  }
+  return {};
 }
 
 /**
  * Get a set of report configurations that all have been marked
  * for scheduled imports.
- * @param {String} opt_user optional user email; if provided, returned
+ * @param {string} opt_user optional user email; if provided, returned
  *   results will only include reports that user is the owner of.
- * @return {Object} collection of configuration object for scheduled
+ * @return {ReportConfig[]} collection of configuration object for scheduled
  *   reports.
  */
 function getScheduledReports(opt_user) {
-  var scheduledReports = [];
-  _.keys(getAllReports()).forEach(function(reportId) {
-    var config = getReportConfig(reportId);
-    if (config && config.scheduled &&
-      (!opt_user || opt_user == config.owner)) {
-      scheduledReports.push(config);
-    }
-  });
+  const scheduledReports = [];
+  if (typeof _ === 'undefined') {
+    throw new Error('Underscore library not found. Have you added it?');
+  }
+  var allReports = getAllReports();
+  if (allReports) {
+    Object.keys(allReports).forEach(function(reportId) {
+      var config = getReportConfig(reportId);
+      if (
+        config &&
+        config.scheduled &&
+        (!opt_user || opt_user == config.owner)
+      ) {
+        scheduledReports.push(config);
+      }
+    });
+  }
   return scheduledReports;
 }
 
 /**
  * Updates the current report list (adding or removing a given
  * report name and id).
- * @param {Number} updateType Enum: either UPDATE_TYPE.ADD or
+ * @param {number} updateType Enum: either UPDATE_TYPE.ADD or
  *   UPDATE_TYPE.REMOVE.
- * @param {String} reportId report to add or remove.
- * @param {String} reportName report name (only needed for ADD).
+ * @param {string} reportId report to add or remove.
+ * @param {string=} reportName report name (only needed for ADD).
  */
 function updateReportSet(updateType, reportId, reportName) {
   var properties = PropertiesService.getDocumentProperties();
   var lock = LockService.getDocumentLock();
   lock.waitLock(2000);
-  var reportSet = JSON.parse(properties.getProperty(REPORT_SET_KEY));
+  var reportSet = getAllReports();
   if (reportSet == null) {
     reportSet = {};
   }
@@ -164,29 +200,37 @@ function updateReportSet(updateType, reportId, reportName) {
  * Update a report configuration with a sheetId and last runtime
  * information, save and return it. Include but do not save the
  * sheet name.
- * @param {Object} config the report configuration.
- * @param {Sheet} sheet the report's sheet.
- * @param {String} lastRun the datetime string indicating the last
+ * @param {ReportConfig} config the report configuration.
+ * @param {GoogleAppsScript.Spreadsheet.Sheet} sheet the report's sheet.
+ * @param {string} lastRun the datetime string indicating the last
  *   time the report was run.
- * @return {Object} the updated report configuration.
+ * @return {ReportConfig} the updated report configuration.
  */
 function updateOnImport(config, sheet, lastRun) {
+  if (typeof _ === 'undefined') {
+    throw new Error('Underscore library not found. Have you added it?');
+  }
   var update = {
     sheetId: sheet.getSheetId().toString(),
-    lastRun: lastRun
+    lastRun: lastRun,
   };
   saveObjectToProperties(config.reportId, update);
-  update.sheetName = sheet.getName();
-  return _.extend(config, update);
+  config.sheetId = update.sheetId;
+  config.lastRun = update.lastRun;
+  config.sheetName = sheet.getName();
+  return config;
 }
 
 /**
  * Return the array of column IDs used by the given report
  * configuration.
- * @param {Object} config the report configuration.
- * @return {Array} column ID strings.
+ * @param {ReportConfig} config the report configuration.
+ * @return {string[]} column ID strings.
  */
 function getColumnIds(config) {
+  if (typeof _ === 'undefined') {
+    throw new Error('Underscore library not found. Have you added it?');
+  }
   return _.map(config.columns, function(col) {
     return col.column;
   });
@@ -203,7 +247,7 @@ function getTriggerId() {
 
 /**
  * Save the trigger ID of the scheduling trigger for this user.
- * @param {Trigger} trigger the trigger whose ID should be saved.
+ * @param {object} trigger the trigger whose ID should be saved.
  */
 function saveTriggerId(trigger) {
   var properties = PropertiesService.getUserProperties();
diff --git a/templates/sheets-import/Server.gs b/templates/sheets-import/Server.gs
index aeca91075..d160503e7 100644
--- a/templates/sheets-import/Server.gs
+++ b/templates/sheets-import/Server.gs
@@ -1,3 +1,4 @@
+// @ts-nocheck
 /**
  * Copyright 2015 Google Inc. All Rights Reserved.
  *
@@ -18,7 +19,12 @@
  * @OnlyCurrentDoc  Limits the script to only accessing the current spreadsheet.
  */
 
-var _ = Underscore.load();
+if (typeof Underscore === 'undefined') {
+  throw new Error('Underscore library not found. Have you added it?');
+}
+// @ts-nocheck
+var Underscore = undefined;
+var _ = undefined;
 
 /**
  * TODO: Replace the following with the name of the service you are importing
@@ -37,12 +43,12 @@ var ERROR_CODES = {
   AUTO_UPDATE_LIMIT: 1,
   ILLEGAL_EDIT: 2,
   ILLEGAL_DELETE: 3,
-  IMPORT_FAILED: 4
+  IMPORT_FAILED: 4,
 };
 
 /**
  * Adds a custom menu with items to show the sidebar.
- * @param {Object} e The event parameter for a simple onOpen trigger.
+ * @param {any} e The event parameter for a simple onOpen trigger.
  */
 function onOpen(e) {
   SpreadsheetApp.getUi()
@@ -54,7 +60,7 @@ function onOpen(e) {
 /**
  * Runs when the add-on is installed; calls onOpen() to ensure menu creation and
  * any other initializion work is done immediately.
- * @param {Object} e The event parameter for a simple onInstall trigger.
+ * @param {any} e The event parameter for a simple onInstall trigger.
  */
 function onInstall(e) {
   onOpen(e);
@@ -74,30 +80,38 @@ function showSidebar() {
   if (!template.isAuthorized) {
     template.authorizationUrl = service.getAuthorizationUrl();
   }
-  var page = template.evaluate()
-      .setTitle(SIDEBAR_TITLE);
+  var page = template.evaluate().setTitle(SIDEBAR_TITLE);
   SpreadsheetApp.getUi().showSidebar(page);
 }
 
+/**
+ * @typedef {{
+ *  name: string,
+ *  reportId: string
+ * }} ReportListItem
+ */
+
 /**
  * Return data needed to build the sidebar UI: a list of the names of the
  * currently saved report configurations and the list of potential
  * column choices.
- * @return {Object} a collection of saved report data and column options.
+ * @return {{reports: ReportListItem[], columns: ColumnOption[]}} a collection
+ * of saved report data and column options.
  */
 function getInitialDataForSidebar() {
   var reportSet = getAllReports();
+  /** @type {ReportListItem[]} */
   var reportList = [];
-  _.each(reportSet, function(val, key) {
-    reportList.push({'name': val, 'reportId': key});
+  Object.keys(reportSet).forEach(function(key) {
+    reportList.push({name: reportSet[key], reportId: key});
   });
   reportList.sort(function(a, b) {
     if (a.name > b.name) {
- return 1;
-}
+      return 1;
+    }
     if (a.name < b.name) {
- return -1;
-}
+      return -1;
+    }
     return 0;
   });
   return {reports: reportList, columns: getColumnOptions()};
@@ -106,12 +120,14 @@ function getInitialDataForSidebar() {
 /**
  * Get the report configuration for the given report and, if a sheet
  * exists for it, activate that sheet.
- * @param {String} reportId a report ID.
- * @return {object} The report config.
+ * @param {string} reportId a report ID.
+ * @return {ReportConfig|null} The report config.
  */
 function switchToReport(reportId) {
   var config = getReportConfig(reportId);
-  activateById(config.sheetId);
+  if (config) {
+    activateById(parseInt(config.sheetId));
+  }
   return config;
 }
 
@@ -119,12 +135,14 @@ function switchToReport(reportId) {
  * Import data to the spreadsheet according to the given report
  * configuration.
  * @param {string} reportId the report identifier.
- * @return {object} the (possibly updated) report configuration.
+ * @return {ReportConfig} the (possibly updated) report configuration.
  */
 function runImport(reportId) {
   var ss = SpreadsheetApp.getActiveSpreadsheet();
   var config = getReportConfig(reportId);
-
+  if (!config) {
+    return;
+  }
   // Acquire the sheet to place the import results in,
   // then clear and format it.
   // Update the saved config with sheet/time information.
@@ -137,21 +155,19 @@ function runImport(reportId) {
   // page at a time.
   var pageNumber = 0;
   var firstRow = 2;
-  try {
-    var page;
-    do {
-      page = getDataPage(columnIds, pageNumber, IMPORT_PAGE_SIZE, config);
-      if (page) {
-        sheet.getRange(firstRow, 1, page.length, page[0].length).setValues(page);
-        firstRow += page.length;
-        pageNumber++;
-        SpreadsheetApp.flush();
-      }
-    } while (page != null);
-  } catch (e) {
-    // Ensure a new sheet Id, if created, is preserved.
-    throw ERROR_CODES.IMPORT_FAILED;
-  }
+
+  var page;
+  do {
+    page = getDataPage(columnIds, pageNumber, IMPORT_PAGE_SIZE, config);
+    if (page && page.length > 0) {
+      sheet
+          .getRange(firstRow, 1, page.length, page[0].length)
+          .setValues(page);
+      firstRow += page.length;
+      pageNumber++;
+      SpreadsheetApp.flush();
+    }
+  } while (page != null);
 
   for (var i = 1; i <= sheet.getLastColumn(); i++) {
     sheet.autoResizeColumn(i);
@@ -162,13 +178,13 @@ function runImport(reportId) {
 
 /**
  * Save the given report configuration.
- * @param {Object} config a report configuration to save.
- * @return {Object} the updated report configuration.
+ * @param {ReportConfig} config a report configuration to save.
+ * @return {ReportConfig} the updated report configuration.
  */
 function saveReport(config) {
   var existingConfig = getReportConfig(config.reportId);
   if (existingConfig != null) {
-    activateById(existingConfig.sheetId);
+    activateById(parseInt(existingConfig.sheetId));
     // Check: users are not allowed to save edits to reports
     // created by other users if those reports have been marked
     // for auto-update.
@@ -188,13 +204,17 @@ function saveReport(config) {
 
 /**
  * Delete the given report configuration.
- * @param {String} reportId indicates the report to delete.
- * @return {String} the report ID deleted.
+ * @param {string} reportId indicates the report to delete.
+ * @return {string} the report ID deleted.
  */
 function removeReport(reportId) {
+  var config = getReportConfig(reportId);
+  if (!config) {
+    return;
+  }
   // Check: users are not allowed to delete reports created by
   // other users if those reports have been marked for auto-update.
-  if (!canEditReport(getReportConfig(reportId))) {
+  if (!canEditReport(config)) {
     throw ERROR_CODES.ILLEGAL_DELETE;
   }
   deleteReportConfig(reportId);
@@ -206,8 +226,8 @@ function removeReport(reportId) {
  * Activate, clear, format and return the sheet associated with the
  * specified report configuration. If the sheet does not exist, create,
  * format and activate it.
- * @param {Object} config the report configuration.
- * @return {Sheet}
+ * @param {ReportConfig} config the report configuration.
+ * @return {GoogleAppsScript.Spreadsheet.Sheet}
  */
 function activateReportSheet(config) {
   var ss = SpreadsheetApp.getActiveSpreadsheet();
@@ -224,10 +244,11 @@ function activateReportSheet(config) {
   sheet.clear();
   sheet.clearNotes();
   sheet.setFrozenRows(1);
-  sheet.getRange('1:1')
-    .setFontWeight('bold')
-    .setBackground('#000000')
-    .setFontColor('#ffffff');
+  sheet
+      .getRange('1:1')
+      .setFontWeight('bold')
+      .setBackground('#000000')
+      .setFontColor('#ffffff');
   sheet.getRange(1, 1, 1, headers.length).setValues([headers]);
   return sheet;
 }
diff --git a/templates/sheets-import/Utilities.gs b/templates/sheets-import/Utilities.gs
index 080beb63f..caefefe82 100644
--- a/templates/sheets-import/Utilities.gs
+++ b/templates/sheets-import/Utilities.gs
@@ -1,3 +1,4 @@
+// @ts-nocheck
 /**
  * Copyright 2015 Google Inc. All Rights Reserved.
  *
@@ -20,6 +21,7 @@
  * @param {string} filename Project file name.
  * @return {string} The content of the rendered HTML.
  */
+// @ts-nocheck
 function include(filename) {
   return HtmlService.createHtmlOutputFromFile(filename).getContent();
 }
@@ -27,28 +29,31 @@ function include(filename) {
 /**
  * Returns true if the given date string represents a date that is
  * more than 24 hours in the past; returns false otherwise.
- * @param {String} dateStr a date string.
- * @return {Boolean}
+ * @param {string} dateStr a date string.
+ * @return {boolean}
  */
 function isOlderThanADay(dateStr) {
-  var now = (new Date()).getTime();
+  var now = new Date().getTime();
   var then = Date.parse(dateStr);
-  return (then + 24 * 60 * 60 * 1000) < now;
+  return then + 24 * 60 * 60 * 1000 < now;
 }
 
 /**
  * Given an object and a string prefix, save every value in that object
  * to the Document properties service as a JSONified string. The property
  * key for each object key will be: prefix.<object_key>
- * @param {String} prefix a common string to label each added property.
- * @param {Object} obj a collection of key-values to save as
+ * @param {string} prefix a common string to label each added property.
+ * @param {Object<string, any>} obj a collection of key-values to save as
  *   user properties.
  */
 function saveObjectToProperties(prefix, obj) {
+  if (typeof _ === 'undefined') {
+    throw new Error('Underscore library not found. Have you added it?');
+  }
   var properties = PropertiesService.getDocumentProperties();
-  _.each(obj, function(val, key) {
-      var propKey = prefix + '.' + key;
-      properties.setProperty(propKey, JSON.stringify(val));
+  Object.keys(obj).forEach(function(key) {
+    var propKey = prefix + '.' + key;
+    properties.setProperty(propKey, JSON.stringify(obj[key]));
   });
 }
 
@@ -57,19 +62,23 @@ function saveObjectToProperties(prefix, obj) {
  * properties whose keys start with that prefix, and return the (JSON-parsed)
  * values in an object. The keys of the returned object will be the
  * same as the property keys with the leading "prefix." removed.
- * @param {String} prefix label of requested properties.
- * @return {Object} collection of key-value pairs taken from the
+ * @param {string} prefix label of requested properties.
+ * @return {Object<string, any>|null} collection of key-value pairs taken from the
  *   properties service. Will return null if the prefix is unrecognized.
  */
 function getObjectFromProperties(prefix) {
+  if (typeof _ === 'undefined') {
+    throw new Error('Underscore library not found. Have you added it?');
+  }
   var properties = PropertiesService.getDocumentProperties();
   var obj = {};
-  _.each(properties.getProperties(), function(val, key) {
+  var allProps = properties.getProperties();
+  Object.keys(allProps).forEach(function(key) {
     if (key.indexOf(prefix) > -1) {
-      obj[key.substr(prefix.length + 1)] = JSON.parse(val);
+      obj[key.substr(prefix.length + 1)] = JSON.parse(allProps[key] || '{}');
     }
   });
-  if (_.keys(obj).length == 0) {
+  if (Object.keys(obj).length == 0) {
     return null;
   }
   return obj;
@@ -78,11 +87,11 @@ function getObjectFromProperties(prefix) {
 /**
  * Given a string prefix, remove from the Document properties service all
  * properties whose keys start with that prefix.
- * @param {String} prefix label of properties to remove.
+ * @param {string} prefix label of properties to remove.
  */
 function deleteObjectFromProperties(prefix) {
   var properties = PropertiesService.getDocumentProperties();
-  _.each(properties.getProperties(), function(val, key) {
+  Object.keys(properties.getProperties()).forEach(function(key) {
     if (key.indexOf(prefix) > -1) {
       properties.deleteProperty(key);
     }
@@ -91,7 +100,7 @@ function deleteObjectFromProperties(prefix) {
 
 /**
  * Generate a random alphanumeric string.
- * @return {String} report ID string.
+ * @return {string} report ID string.
  */
 function newReportId() {
   return Math.random().toString(36).substring(2);
@@ -100,9 +109,9 @@ function newReportId() {
 /**
  * Sheets-specific utility. Find a sheet within a spreadsheet with
  * the given id. If not present, return null.
- * @param {Object} ss a Spreadsheet object.
- * @param {Number} sheetId a Sheet id.
- * @return {Object} a Sheet object, or null if not found.
+ * @param {object} ss a Spreadsheet object.
+ * @param {number} sheetId a Sheet id.
+ * @return {object|null} a Sheet object, or null if not found.
  */
 function getSheetById(ss, sheetId) {
   if (sheetId === null) {
@@ -123,16 +132,16 @@ function getSheetById(ss, sheetId) {
  * suffix to append to it to make it unique and return. This function
  * is used to avoid name collisions while adding or renaming sheets
  * automatically.
- * @param {Object} spreadsheet a Spreadsheet.
- * @param {String} baseName the initial suggested title for a sheet.
- * @return {String} a unique title for the sheet, based on the
+ * @param {object} spreadsheet a Spreadsheet.
+ * @param {string} baseName the initial suggested title for a sheet.
+ * @return {string} a unique title for the sheet, based on the
  *     given base title.
  */
 function getUniqueSheetName(spreadsheet, baseName) {
   var sheetName = baseName;
   var i = 2;
   while (spreadsheet.getSheetByName(sheetName) != null) {
-      sheetName = baseName + ' ' + i++;
+    sheetName = baseName + ' ' + i++;
   }
   return sheetName;
 }
@@ -141,9 +150,9 @@ function getUniqueSheetName(spreadsheet, baseName) {
  * Sheets-specific utility. Given a spreadsheet and a triggerId string,
  * return the user trigger that corresponds to that ID. Returns null
  * if no such trigger exists.
- * @param {Spreadsheet} spreadsheet container of the user triggers.
- * @param {String} triggerId trigger ID string.
- * @return {Trigger} corresponding user trigger, or null if not found.
+ * @param {object} spreadsheet container of the user triggers.
+ * @param {string} triggerId trigger ID string.
+ * @return {object|null} corresponding user trigger, or null if not found.
  */
 function getUserTriggerById(spreadsheet, triggerId) {
   var triggers = ScriptApp.getUserTriggers(spreadsheet);
@@ -158,11 +167,11 @@ function getUserTriggerById(spreadsheet, triggerId) {
 /**
  * Sheets-specific utility. Given a String sheet id, activate that
  * sheet if it exists.
- * @param {String} sheetId the sheet ID.
+ * @param {number} sheetId the sheet ID.
  */
 function activateById(sheetId) {
   var ss = SpreadsheetApp.getActiveSpreadsheet();
-  var sheet = getSheetById(ss, parseInt(sheetId));
+  var sheet = getSheetById(ss, sheetId);
   if (sheet != null) {
     sheet.activate();
   }
diff --git a/templates/standalone/helloWorld.gs b/templates/standalone/helloWorld.gs
index a9794babf..215d4c8ba 100644
--- a/templates/standalone/helloWorld.gs
+++ b/templates/standalone/helloWorld.gs
@@ -16,32 +16,30 @@
 // [START apps_script_hello_world]
 /**
  * Creates a Google Doc and sends an email to the current user with a link to the doc.
+ * @return {void}
  */
 function createAndSendDocument() {
-  try {
-    // Create a new Google Doc named 'Hello, world!'
-    const doc = DocumentApp.create('Hello, world!');
+  // Create a new Google Doc named 'Hello, world!'
+  const doc = DocumentApp.create('Hello, world!');
 
-    // Access the body of the document, then add a paragraph.
-    doc.getBody().appendParagraph('This document was created by Google Apps Script.');
+  // Access the body of the document, then add a paragraph.
+  doc
+      .getBody()
+      .appendParagraph('This document was created by Google Apps Script.');
 
-    // Get the URL of the document.
-    const url = doc.getUrl();
+  // Get the URL of the document.
+  const url = doc.getUrl();
 
-    // Get the email address of the active user - that's you.
-    const email = Session.getActiveUser().getEmail();
+  // Get the email address of the active user - that's you.
+  const email = Session.getActiveUser().getEmail();
 
-    // Get the name of the document to use as an email subject line.
-    const subject = doc.getName();
+  // Get the name of the document to use as an email subject line.
+  const subject = doc.getName();
 
-    // Append a new string to the "url" variable to use as an email body.
-    const body = 'Link to your doc: ' + url;
+  // Append a new string to the "url" variable to use as an email body.
+  const body = 'Link to your doc: ' + url;
 
-    // Send yourself an email with a link to the document.
-    GmailApp.sendEmail(email, subject, body);
-  } catch (err) {
-    // TODO (developer) - Handle exception
-    console.log('Failed with error %s', err.message);
-  }
+  // Send yourself an email with a link to the document.
+  GmailApp.sendEmail(email, subject, body);
 }
 // [END apps_script_hello_world]
diff --git a/templates/web-app/Code.gs b/templates/web-app/Code.gs
index 57bf21b16..866ba20ac 100644
--- a/templates/web-app/Code.gs
+++ b/templates/web-app/Code.gs
@@ -14,15 +14,23 @@
  * limitations under the License.
  */
 
+/**
+ * @typedef {{
+ *   parameter: {
+ *     folderId: string,
+ *   }
+ * }} AppsScriptEvent
+ */
+
 /**
  * Serves HTML of the application for HTTP GET requests.
  * If folderId is provided as a URL parameter, the web app will list
  * the contents of that folder (if permissions allow). Otherwise
  * the web app will list the contents of the root folder.
  *
- * @param {Object} e event parameter that can contain information
+ * @param {AppsScriptEvent} e event parameter that can contain information
  *     about any URL parameters provided.
- * @return {HTML} The web app's HTML.
+ * @return {object} The web app's HTML.
  */
 function doGet(e) {
   var template = HtmlService.createTemplateFromFile('Index');
@@ -35,24 +43,32 @@ function doGet(e) {
   }
 
   // Build and return HTML in IFRAME sandbox mode.
-  return template.evaluate()
-      .setTitle('Web App Window Title');
+  return template.evaluate().setTitle('Web App Window Title');
 }
 
+/**
+ * @typedef {{
+ *   children: string[],
+ *   rootName: string,
+ * }} FolderContents
+ */
+
 /**
  * Return an array of up to 20 filenames contained in the
  * folder previously specified (or the root folder by default).
  *
- * @param {String} folderId String ID of folder whose contents
+ * @param {string} folderId String ID of folder whose contents
  *     are to be retrieved; if this is 'root', the
  *     root folder is used.
- * @return {Object} list of content filenames, along with
+ * @return {FolderContents} list of content filenames, along with
  *     the root folder name.
  */
 function getFolderContents(folderId) {
   var topFolder;
+  /** @type {FolderContents} */
   var contents = {
-    children: []
+    children: [],
+    rootName: '',
   };
 
   if (folderId == 'root') {