diff --git a/blocks/lists.ts b/blocks/lists.ts
index d115a321c..3b468dc9d 100644
--- a/blocks/lists.ts
+++ b/blocks/lists.ts
@@ -227,7 +227,7 @@ const LISTS_CREATE_WITH = {
     // Disconnect any children that don't belong.
     for (let i = 0; i < this.itemCount_; i++) {
       const connection = this.getInput('ADD' + i)!.connection!.targetConnection;
-      if (connection && connections.indexOf(connection) === -1) {
+      if (connection && !connections.includes(connection)) {
         connection.disconnect();
       }
     }
diff --git a/blocks/procedures.ts b/blocks/procedures.ts
index 25fe240b8..1457971d8 100644
--- a/blocks/procedures.ts
+++ b/blocks/procedures.ts
@@ -858,7 +858,7 @@ const PROCEDURE_CALL_COMMON = {
         if (
           mutatorOpen &&
           connection &&
-          paramIds.indexOf(this.quarkIds_[i]) === -1
+          !paramIds.includes(this.quarkIds_[i])
         ) {
           // This connection should no longer be attached to this block.
           connection.disconnect();
@@ -1041,7 +1041,7 @@ const PROCEDURE_CALL_COMMON = {
     }
     if (
       event.type === Events.BLOCK_CREATE &&
-      (event as BlockCreate).ids!.indexOf(this.id) !== -1
+      (event as BlockCreate).ids!.includes(this.id)
     ) {
       // Look for the case where a procedure call was created (usually through
       // paste) and there is no matching definition.  In this case, create
@@ -1286,7 +1286,7 @@ const PROCEDURES_IFRETURN = {
     // Is the block nested in a procedure?
     let block = this; // eslint-disable-line @typescript-eslint/no-this-alias
     do {
-      if (this.FUNCTION_TYPES.indexOf(block.type) !== -1) {
+      if (this.FUNCTION_TYPES.includes(block.type)) {
         legal = true;
         break;
       }
diff --git a/blocks/text.ts b/blocks/text.ts
index e0470c169..91a27005a 100644
--- a/blocks/text.ts
+++ b/blocks/text.ts
@@ -796,7 +796,7 @@ const JOIN_MUTATOR_MIXIN = {
     // Disconnect any children that don't belong.
     for (let i = 0; i < this.itemCount_; i++) {
       const connection = this.getInput('ADD' + i)!.connection!.targetConnection;
-      if (connection && connections.indexOf(connection) === -1) {
+      if (connection && !connections.includes(connection)) {
         connection.disconnect();
       }
     }
diff --git a/core/block.ts b/core/block.ts
index 82c82cb43..a321ad141 100644
--- a/core/block.ts
+++ b/core/block.ts
@@ -1529,8 +1529,7 @@ export class Block implements IASTNodeLocation, IDeletable {
         checks = connection.targetConnection.getCheck();
       }
       return (
-        !!checks &&
-        (checks.indexOf('Boolean') !== -1 || checks.indexOf('Number') !== -1)
+        !!checks && (checks.includes('Boolean') || checks.includes('Number'))
       );
     }
 
diff --git a/core/bump_objects.ts b/core/bump_objects.ts
index 39fcd0a50..d06b66800 100644
--- a/core/bump_objects.ts
+++ b/core/bump_objects.ts
@@ -99,7 +99,7 @@ export function bumpIntoBoundsHandler(
       return;
     }
 
-    if (eventUtils.BUMP_EVENTS.indexOf(e.type ?? '') !== -1) {
+    if (eventUtils.BUMP_EVENTS.includes(e.type ?? '')) {
       const scrollMetricsInWsCoords = metricsManager.getScrollMetrics(true);
 
       // Triggered by move/create event
diff --git a/core/component_manager.ts b/core/component_manager.ts
index 9bb66fcbb..b9654c94e 100644
--- a/core/component_manager.ts
+++ b/core/component_manager.ts
@@ -172,7 +172,7 @@ export class ComponentManager {
     capability = `${capability}`.toLowerCase();
     return (
       this.componentData.has(id) &&
-      this.componentData.get(id)!.capabilities.indexOf(capability) !== -1
+      this.componentData.get(id)!.capabilities.includes(capability)
     );
   }
 
diff --git a/core/connection_checker.ts b/core/connection_checker.ts
index f7d09b972..6f5ecd5d5 100644
--- a/core/connection_checker.ts
+++ b/core/connection_checker.ts
@@ -210,7 +210,7 @@ export class ConnectionChecker implements IConnectionChecker {
     }
     // Find any intersection in the check lists.
     for (let i = 0; i < checkArrayOne.length; i++) {
-      if (checkArrayTwo.indexOf(checkArrayOne[i]) !== -1) {
+      if (checkArrayTwo.includes(checkArrayOne[i])) {
         return true;
       }
     }
@@ -298,7 +298,7 @@ export class ConnectionChecker implements IConnectionChecker {
     }
 
     // Don't let blocks try to connect to themselves or ones they nest.
-    if (common.draggingConnections.indexOf(b) !== -1) {
+    if (common.draggingConnections.includes(b)) {
       return false;
     }
 
@@ -321,7 +321,7 @@ export class ConnectionChecker implements IConnectionChecker {
     }
 
     // Don't let blocks try to connect to themselves or ones they nest.
-    if (common.draggingConnections.indexOf(b) !== -1) {
+    if (common.draggingConnections.includes(b)) {
       return false;
     }
 
diff --git a/core/extensions.ts b/core/extensions.ts
index 6313c4161..aa9a6a186 100644
--- a/core/extensions.ts
+++ b/core/extensions.ts
@@ -401,7 +401,7 @@ export function buildTooltipForDropdown(
   const blockTypesChecked: string[] = [];
 
   return function (this: Block) {
-    if (blockTypesChecked.indexOf(this.type) === -1) {
+    if (!blockTypesChecked.includes(this.type)) {
       checkDropdownOptionsInTable(this, dropdownName, lookupTable);
       blockTypesChecked.push(this.type);
     }
diff --git a/core/field_dropdown.ts b/core/field_dropdown.ts
index ad728f226..6fb779c4f 100644
--- a/core/field_dropdown.ts
+++ b/core/field_dropdown.ts
@@ -408,7 +408,13 @@ export class FieldDropdown extends Field<string> {
    * @param newValue The input value.
    * @returns A valid language-neutral option, or null if invalid.
    */
-  protected override doClassValidation_(newValue?: string): string | null {
+  protected override doClassValidation_(
+    newValue: string,
+  ): string | null | undefined;
+  protected override doClassValidation_(newValue?: string): string | null;
+  protected override doClassValidation_(
+    newValue?: string,
+  ): string | null | undefined {
     const options = this.getOptions(true);
     const isValueValid = options.some((option) => option[1] === newValue);
 
@@ -426,7 +432,7 @@ export class FieldDropdown extends Field<string> {
       }
       return null;
     }
-    return newValue as string;
+    return newValue;
   }
 
   /**
diff --git a/core/field_number.ts b/core/field_number.ts
index 8965dd330..ee04eab49 100644
--- a/core/field_number.ts
+++ b/core/field_number.ts
@@ -216,7 +216,7 @@ export class FieldNumber extends FieldInput<number> {
   private setPrecisionInternal(precision: number | string | undefined | null) {
     this.precision_ = Number(precision) || 0;
     let precisionString = String(this.precision_);
-    if (precisionString.indexOf('e') !== -1) {
+    if (precisionString.includes('e')) {
       // String() is fast.  But it turns .0000001 into '1e-7'.
       // Use the much slower toLocaleString to access all the digits.
       precisionString = this.precision_.toLocaleString('en-US', {
diff --git a/core/flyout_base.ts b/core/flyout_base.ts
index 438e92d64..360b3ac2f 100644
--- a/core/flyout_base.ts
+++ b/core/flyout_base.ts
@@ -1201,7 +1201,7 @@ export abstract class Flyout
   private filterForCapacity() {
     const blocks = this.workspace_.getTopBlocks(false);
     for (let i = 0, block; (block = blocks[i]); i++) {
-      if (this.permanentlyDisabled.indexOf(block) === -1) {
+      if (!this.permanentlyDisabled.includes(block)) {
         const enable = this.targetWorkspace.isCapacityAvailable(
           common.getBlockTypeCounts(block),
         );
diff --git a/core/generator.ts b/core/generator.ts
index 35a962396..a24a04697 100644
--- a/core/generator.ts
+++ b/core/generator.ts
@@ -568,11 +568,7 @@ export class CodeGenerator {
    * @param _opt_thisOnly True to generate code for only this statement.
    * @returns Code with comments and subsequent blocks added.
    */
-  protected scrub_(
-    _block: Block,
-    code: string,
-    _opt_thisOnly?: boolean,
-  ): string {
+  scrub_(_block: Block, code: string, _opt_thisOnly?: boolean): string {
     // Optionally override
     return code;
   }
diff --git a/core/names.ts b/core/names.ts
index ce8c626db..4f4c72faa 100644
--- a/core/names.ts
+++ b/core/names.ts
@@ -218,7 +218,7 @@ export class Names {
       // https://github.com/google/blockly/issues/1654
       name = encodeURI(name.replace(/ /g, '_')).replace(/[^\w]/g, '_');
       // Most languages don't allow names with leading numbers.
-      if ('0123456789'.indexOf(name[0]) !== -1) {
+      if ('0123456789'.includes(name[0])) {
         name = 'my_' + name;
       }
     }
diff --git a/core/renderers/common/constants.ts b/core/renderers/common/constants.ts
index 1983793f0..078fc01d6 100644
--- a/core/renderers/common/constants.ts
+++ b/core/renderers/common/constants.ts
@@ -617,7 +617,7 @@ export class ConstantProvider {
   getBlockStyle(blockStyleName: string | null): BlockStyle {
     return (
       this.blockStyles[blockStyleName || ''] ||
-      (blockStyleName && blockStyleName.indexOf('auto_') === 0
+      (blockStyleName && blockStyleName.startsWith('auto_')
         ? this.getBlockStyleForColour(blockStyleName.substring(5)).style
         : this.createBlockStyle_('#000000'))
     );
diff --git a/core/renderers/zelos/constants.ts b/core/renderers/zelos/constants.ts
index 1eabd7edd..f16ca8098 100644
--- a/core/renderers/zelos/constants.ts
+++ b/core/renderers/zelos/constants.ts
@@ -536,13 +536,13 @@ export class ConstantProvider extends BaseConstantProvider {
           }
         }
         // Includes doesn't work in IE.
-        if (checks && checks.indexOf('Boolean') !== -1) {
+        if (checks && checks.includes('Boolean')) {
           return this.HEXAGONAL!;
         }
-        if (checks && checks.indexOf('Number') !== -1) {
+        if (checks && checks.includes('Number')) {
           return this.ROUNDED!;
         }
-        if (checks && checks.indexOf('String') !== -1) {
+        if (checks && checks.includes('String')) {
           return this.ROUNDED!;
         }
         return this.ROUNDED!;
diff --git a/core/shortcut_registry.ts b/core/shortcut_registry.ts
index 556efb148..35f409b48 100644
--- a/core/shortcut_registry.ts
+++ b/core/shortcut_registry.ts
@@ -325,7 +325,7 @@ export class ShortcutRegistry {
         const modifierKeyCode = (
           ShortcutRegistry.modifierKeys as AnyDuringMigration
         )[modifier];
-        if (modifiers.indexOf(modifierKeyCode) > -1) {
+        if (modifiers.includes(modifierKeyCode)) {
           if (serializedKey !== '') {
             serializedKey += '+';
           }
diff --git a/core/trashcan.ts b/core/trashcan.ts
index 42c32ea1f..b48777c4d 100644
--- a/core/trashcan.ts
+++ b/core/trashcan.ts
@@ -616,7 +616,7 @@ export class Trashcan
       const cleanedJson = JSON.stringify(
         this.cleanBlockJson(deleteEvent.oldJson),
       );
-      if (this.contents.indexOf(cleanedJson) !== -1) {
+      if (this.contents.includes(cleanedJson)) {
         return;
       }
       this.contents.unshift(cleanedJson);
diff --git a/core/utils/string.ts b/core/utils/string.ts
index fbe9f5210..b7842c948 100644
--- a/core/utils/string.ts
+++ b/core/utils/string.ts
@@ -204,9 +204,9 @@ function wrapScore(
     score -= Math.pow(maxLength - lineLengths[i], 1.5);
     // Optimize for structure.
     // Add score to line endings after punctuation.
-    if ('.?!'.indexOf(linePunctuation[i]) !== -1) {
+    if ('.?!'.includes(linePunctuation[i])) {
       score += limit / 3;
-    } else if (',;)]}'.indexOf(linePunctuation[i]) !== -1) {
+    } else if (',;)]}'.includes(linePunctuation[i])) {
       score += limit / 4;
     }
   }
diff --git a/core/utils/svg_math.ts b/core/utils/svg_math.ts
index bb095932f..88d38f625 100644
--- a/core/utils/svg_math.ts
+++ b/core/utils/svg_math.ts
@@ -62,7 +62,7 @@ export function getRelativeXY(element: Element): Coordinate {
 
   // Then check for style = transform: translate(...) or translate3d(...)
   const style = element.getAttribute('style');
-  if (style && style.indexOf('translate') > -1) {
+  if (style && style.includes('translate')) {
     const styleComponents = style.match(XY_STYLE_REGEX);
     if (styleComponents) {
       xy.x += Number(styleComponents[1]);
@@ -90,7 +90,7 @@ export function getInjectionDivXY(element: Element): Coordinate {
     x = x + xy.x;
     y = y + xy.y;
     const classes = element.getAttribute('class') || '';
-    if ((' ' + classes + ' ').indexOf(' injectionDiv ') !== -1) {
+    if ((' ' + classes + ' ').includes(' injectionDiv ')) {
       break;
     }
     element = element.parentNode as Element;
diff --git a/core/utils/toolbox.ts b/core/utils/toolbox.ts
index 699150f1c..17fd327c6 100644
--- a/core/utils/toolbox.ts
+++ b/core/utils/toolbox.ts
@@ -381,7 +381,7 @@ function addAttributes(node: Node, obj: AnyDuringMigration) {
     // AnyDuringMigration because:  Property 'attributes' does not exist on type
     // 'Node'.
     const attr = (node as AnyDuringMigration).attributes[j];
-    if (attr.nodeName.indexOf('css-') > -1) {
+    if (attr.nodeName.includes('css-')) {
       obj['cssconfig'] = obj['cssconfig'] || {};
       obj['cssconfig'][attr.nodeName.replace('css-', '')] = attr.value;
     } else {
diff --git a/core/utils/useragent.ts b/core/utils/useragent.ts
index 078d79a66..92180c21d 100644
--- a/core/utils/useragent.ts
+++ b/core/utils/useragent.ts
@@ -37,7 +37,7 @@ let isMobile: boolean;
    * @returns True if name is present.
    */
   function has(name: string): boolean {
-    return rawUpper.indexOf(name.toUpperCase()) !== -1;
+    return rawUpper.includes(name.toUpperCase());
   }
 
   // Browsers.  Logic from:
diff --git a/core/variables.ts b/core/variables.ts
index 74c2b9252..dee53a72b 100644
--- a/core/variables.ts
+++ b/core/variables.ts
@@ -642,7 +642,7 @@ export function getAddedVariables(
       const variable = allCurrentVariables[i];
       // For any variable that is present in allCurrentVariables but not
       // present in originalVariables, add the variable to addedVariables.
-      if (originalVariables.indexOf(variable) === -1) {
+      if (!originalVariables.includes(variable)) {
         addedVariables.push(variable);
       }
     }
diff --git a/core/workspace_svg.ts b/core/workspace_svg.ts
index f608311d1..2d49485dd 100644
--- a/core/workspace_svg.ts
+++ b/core/workspace_svg.ts
@@ -690,7 +690,7 @@ export class WorkspaceSvg extends Workspace implements IASTNodeLocationSvg {
       let element: Element = this.svgGroup_;
       while (element) {
         const classes = element.getAttribute('class') || '';
-        if ((' ' + classes + ' ').indexOf(' injectionDiv ') !== -1) {
+        if ((' ' + classes + ' ').includes(' injectionDiv ')) {
           this.injectionDiv = element;
           break;
         }
@@ -1301,7 +1301,7 @@ export class WorkspaceSvg extends Workspace implements IASTNodeLocationSvg {
       // Using Set here would be great, but at the cost of IE10 support.
       if (!state) {
         arrayUtils.removeElem(this.highlightedBlocks, block);
-      } else if (this.highlightedBlocks.indexOf(block) === -1) {
+      } else if (!this.highlightedBlocks.includes(block)) {
         this.highlightedBlocks.push(block);
       }
       block.setHighlighted(state);
diff --git a/demos/blockfactory/block_exporter_controller.js b/demos/blockfactory/block_exporter_controller.js
index bd41f2e74..bccd8087d 100644
--- a/demos/blockfactory/block_exporter_controller.js
+++ b/demos/blockfactory/block_exporter_controller.js
@@ -224,9 +224,9 @@ BlockExporterController.prototype.selectUsedBlocks = function() {
   var unstoredCustomBlockTypes = [];
 
   for (var i = 0, blockType; blockType = this.usedBlockTypes[i]; i++) {
-    if (storedBlockTypes.indexOf(blockType) !== -1) {
+    if (storedBlockTypes.includes(blockType)) {
       sharedBlockTypes.push(blockType);
-    } else if (StandardCategories.coreBlockTypes.indexOf(blockType) === -1) {
+    } else if (!StandardCategories.coreBlockTypes.includes(blockType)) {
       unstoredCustomBlockTypes.push(blockType);
     }
   }
diff --git a/demos/blockfactory/blocks.js b/demos/blockfactory/blocks.js
index 70691e264..b93ae5739 100644
--- a/demos/blockfactory/blocks.js
+++ b/demos/blockfactory/blocks.js
@@ -682,7 +682,7 @@ Blockly.Blocks['type_group'] = {
     // Disconnect any children that don't belong.
     for (var i = 0; i < this.typeCount_; i++) {
       var connection = this.getInput('TYPE' + i).connection.targetConnection;
-      if (connection && connections.indexOf(connection) === -1) {
+      if (connection && !connections.includes(connection)) {
         connection.disconnect();
       }
     }
diff --git a/demos/blockfactory/factory.js b/demos/blockfactory/factory.js
index a77d8467a..07ee889de 100644
--- a/demos/blockfactory/factory.js
+++ b/demos/blockfactory/factory.js
@@ -238,7 +238,7 @@ BlockFactory.updatePreview = function() {
     // Warn user only if their block type is already exists in Blockly's
     // standard library.
     var rootBlock = FactoryUtils.getRootBlock(BlockFactory.mainWorkspace);
-    if (StandardCategories.coreBlockTypes.indexOf(blockType) !== -1) {
+    if (StandardCategories.coreBlockTypes.includes(blockType)) {
       rootBlock.setWarningText('A core Blockly block already exists ' +
           'under this name.');
 
diff --git a/demos/blockfactory/factory_utils.js b/demos/blockfactory/factory_utils.js
index 164b3357b..148498360 100644
--- a/demos/blockfactory/factory_utils.js
+++ b/demos/blockfactory/factory_utils.js
@@ -594,7 +594,7 @@ FactoryUtils.getOptTypesFrom = function(block, name) {
   var types = FactoryUtils.getTypesFrom_(block, name);
   if (types.length === 0) {
     return undefined;
-  } else if (types.indexOf('null') !== -1) {
+  } else if (types.includes('null')) {
     return 'null';
   } else if (types.length === 1) {
     return types[0];
@@ -771,7 +771,7 @@ FactoryUtils.parseJsBlockDefinitions = function(blockDefsString) {
   var blockDefArray = [];
   var defStart = blockDefsString.indexOf('Blockly.Blocks');
 
-  while (blockDefsString.indexOf('Blockly.Blocks', defStart) !== -1) {
+  while (blockDefsString.includes('Blockly.Blocks', defStart)) {
     var nextStart = blockDefsString.indexOf('Blockly.Blocks', defStart + 1);
     if (nextStart === -1) {
       // This is the last block definition.
diff --git a/demos/blockfactory/index.html b/demos/blockfactory/index.html
index 14d84d73f..9f33aa4fb 100644
--- a/demos/blockfactory/index.html
+++ b/demos/blockfactory/index.html
@@ -369,7 +369,7 @@
                     // Manual JavaScript works but requires use of eval().
                     // TODO(#1269): Replace eval() with JS-Interpreter before
                     //              re-enabling "Manual JavaScript" mode.
-                    if (document.location.href.indexOf('file://') === 0) {
+                    if (document.location.href.startsWith('file://')) {
                       document.write(
                           '<option value="Manual-JS">Manual JavaScript&hellip;</option>');
                     }
diff --git a/demos/blockfactory/workspacefactory/wfactory_model.js b/demos/blockfactory/workspacefactory/wfactory_model.js
index 9b9586ea1..b0e1ab9d4 100644
--- a/demos/blockfactory/workspacefactory/wfactory_model.js
+++ b/demos/blockfactory/workspacefactory/wfactory_model.js
@@ -395,7 +395,7 @@ WorkspaceFactoryModel.prototype.getAllUsedBlockTypes = function() {
     // Add block types if not already in list.
     for (var i = 0; i < blocks.length; i++) {
       var type = blocks[i].getAttribute('type');
-      if (list.indexOf(type) === -1) {
+      if (!list.includes(type)) {
         list.push(type);
       }
     }
@@ -444,9 +444,9 @@ WorkspaceFactoryModel.prototype.updateLibBlockTypes = function(blockTypes) {
  */
 WorkspaceFactoryModel.prototype.isDefinedBlockType = function(blockType) {
   var isStandardBlock =
-      StandardCategories.coreBlockTypes.indexOf(blockType) !== -1;
-  var isLibBlock = this.libBlockTypes.indexOf(blockType) !== -1;
-  var isImportedBlock = this.importedBlockTypes.indexOf(blockType) !== -1;
+      StandardCategories.coreBlockTypes.includes(blockType);
+  var isLibBlock = this.libBlockTypes.includes(blockType);
+  var isImportedBlock = this.importedBlockTypes.includes(blockType);
   return (isStandardBlock || isLibBlock || isImportedBlock);
 };
 
diff --git a/demos/code/code.js b/demos/code/code.js
index 63b776aab..c264ff2dc 100644
--- a/demos/code/code.js
+++ b/demos/code/code.js
@@ -106,7 +106,7 @@ Code.getLang = function() {
  * @return {boolean} True if RTL, false if LTR.
  */
 Code.isRtl = function() {
-  return Code.LANGUAGE_RTL.indexOf(Code.LANG) !== -1;
+  return Code.LANGUAGE_RTL.includes(Code.LANG);
 };
 
 /**
@@ -396,7 +396,7 @@ Code.checkAllGeneratorFunctionsDefined = function(generator) {
   for (var i = 0; i < blocks.length; i++) {
     var blockType = blocks[i].type;
     if (!generator.forBlock[blockType]) {
-      if (missingBlockGenerators.indexOf(blockType) === -1) {
+      if (!missingBlockGenerators.includes(blockType)) {
         missingBlockGenerators.push(blockType);
       }
     }
@@ -450,7 +450,7 @@ Code.init = function() {
   // TODO: Clean up the message files so this is done explicitly instead of
   // through this for-loop.
   for (var messageKey in MSG) {
-    if (messageKey.indexOf('cat') === 0) {
+    if (messageKey.startsWith('cat')) {
       Blockly.Msg[messageKey.toUpperCase()] = MSG[messageKey];
     }
   }
diff --git a/generators/javascript/javascript_generator.ts b/generators/javascript/javascript_generator.ts
index 02602e71f..592563f91 100644
--- a/generators/javascript/javascript_generator.ts
+++ b/generators/javascript/javascript_generator.ts
@@ -251,7 +251,6 @@ export class JavascriptGenerator extends CodeGenerator {
    * @param code The JavaScript code created for this block.
    * @param thisOnly True to generate code for only this statement.
    * @returns JavaScript code with comments and subsequent blocks added.
-   * @protected
    */
   scrub_(block: Block, code: string, thisOnly = false): string {
     let commentCode = '';
diff --git a/generators/lua/loops.ts b/generators/lua/loops.ts
index fec175b48..01474cd81 100644
--- a/generators/lua/loops.ts
+++ b/generators/lua/loops.ts
@@ -35,7 +35,7 @@ const CONTINUE_STATEMENT = 'goto continue\n';
  * @returns Generated label or '' if unnecessary
  */
 function addContinueLabel(branch: string, indent: string): string {
-  if (branch.indexOf(CONTINUE_STATEMENT) !== -1) {
+  if (branch.includes(CONTINUE_STATEMENT)) {
     // False positives are possible (e.g. a string literal), but are harmless.
     return branch + indent + '::continue::\n';
   } else {
diff --git a/generators/php/procedures.ts b/generators/php/procedures.ts
index 5d44eb21b..bd114cd0d 100644
--- a/generators/php/procedures.ts
+++ b/generators/php/procedures.ts
@@ -27,7 +27,7 @@ export function procedures_defreturn(block: Block, generator: PhpGenerator) {
   for (const variable of usedVariables) {
     const varName = variable.name;
     // getVars returns parameter names, not ids, for procedure blocks
-    if (block.getVars().indexOf(varName) === -1) {
+    if (!block.getVars().includes(varName)) {
       globals.push(generator.getVariableName(varName));
     }
   }
diff --git a/generators/python/procedures.ts b/generators/python/procedures.ts
index 0d9b2e85d..798d6d55a 100644
--- a/generators/python/procedures.ts
+++ b/generators/python/procedures.ts
@@ -27,7 +27,7 @@ export function procedures_defreturn(block: Block, generator: PythonGenerator) {
   for (const variable of usedVariables) {
     const varName = variable.name;
     // getVars returns parameter names, not ids, for procedure blocks
-    if (block.getVars().indexOf(varName) === -1) {
+    if (!block.getVars().includes(varName)) {
       globals.push(generator.getVariableName(varName));
     }
   }
diff --git a/generators/python/python_generator.ts b/generators/python/python_generator.ts
index 229c2022c..bf7b87496 100644
--- a/generators/python/python_generator.ts
+++ b/generators/python/python_generator.ts
@@ -243,8 +243,8 @@ export class PythonGenerator extends CodeGenerator {
 
     // Follow the CPython behaviour of repr() for a non-byte string.
     let quote = "'";
-    if (string.indexOf("'") !== -1) {
-      if (string.indexOf('"') === -1) {
+    if (string.includes("'")) {
+      if (!string.includes('"')) {
         quote = '"';
       } else {
         string = string.replace(/'/g, "\\'");
@@ -276,7 +276,6 @@ export class PythonGenerator extends CodeGenerator {
    * @param code The Python code created for this block.
    * @param thisOnly True to generate code for only this statement.
    * @returns Python code with comments and subsequent blocks added.
-
    */
   scrub_(block: Block, code: string, thisOnly = false): string {
     let commentCode = '';
diff --git a/package-lock.json b/package-lock.json
index 8b87ef3f3..27f77fc0f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -48,7 +48,7 @@
         "prettier": "3.2.5",
         "readline-sync": "^1.4.10",
         "rimraf": "^5.0.0",
-        "typescript": "^5.0.2",
+        "typescript": "^5.3.3",
         "webdriverio": "^8.32.2",
         "yargs": "^17.2.1"
       },
@@ -11017,9 +11017,9 @@
       "dev": true
     },
     "node_modules/typescript": {
-      "version": "5.2.2",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.2.2.tgz",
-      "integrity": "sha512-mI4WrpHsbCIcwT9cF4FZvr80QUeKvsUsUvKDoR+X/7XHQH98xYD8YHZg7ANtz2GtZt/CBq2QJ0thkGJMHfqc1w==",
+      "version": "5.4.2",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.4.2.tgz",
+      "integrity": "sha512-+2/g0Fds1ERlP6JsakQQDXjZdZMM+rqpamFZJEKh4kwTIn3iDkgKtby0CeNd5ATNZ4Ry1ax15TMx0W2V+miizQ==",
       "dev": true,
       "bin": {
         "tsc": "bin/tsc",
diff --git a/package.json b/package.json
index 86ed37072..bb46b884a 100644
--- a/package.json
+++ b/package.json
@@ -131,7 +131,7 @@
     "prettier": "3.2.5",
     "readline-sync": "^1.4.10",
     "rimraf": "^5.0.0",
-    "typescript": "^5.0.2",
+    "typescript": "^5.3.3",
     "webdriverio": "^8.32.2",
     "yargs": "^17.2.1"
   },
diff --git a/scripts/gulpfiles/release_tasks.js b/scripts/gulpfiles/release_tasks.js
index 5a0eb9f0e..f2545c7b9 100644
--- a/scripts/gulpfiles/release_tasks.js
+++ b/scripts/gulpfiles/release_tasks.js
@@ -131,7 +131,7 @@ function updateBetaVersion(done) {
   const latestBetaVersion = execSync('npm show blockly version --tag beta').toString().trim();
   while (!isValid) {
     newVersion = readlineSync.question(`What is the new beta version? (latest beta version: ${latestBetaVersion})`);
-    const existsOnNpm = blocklyVersions.indexOf(newVersion) > -1;
+    const existsOnNpm = blocklyVersions.includes(newVersion);
     const isFormatted = newVersion.search(re) > -1;
     if (!existsOnNpm && isFormatted) {
       isValid = true;
diff --git a/tests/mocha/test_helpers/user_input.js b/tests/mocha/test_helpers/user_input.js
index 6606a6652..a5902a7db 100644
--- a/tests/mocha/test_helpers/user_input.js
+++ b/tests/mocha/test_helpers/user_input.js
@@ -41,10 +41,10 @@ export function createKeyDownEvent(keyCode, modifiers) {
     keyCode: keyCode,
   };
   if (modifiers && modifiers.length > 0) {
-    event.altKey = modifiers.indexOf(KeyCodes.ALT) > -1;
-    event.ctrlKey = modifiers.indexOf(KeyCodes.CTRL) > -1;
-    event.metaKey = modifiers.indexOf(KeyCodes.META) > -1;
-    event.shiftKey = modifiers.indexOf(KeyCodes.SHIFT) > -1;
+    event.altKey = modifiers.includes(KeyCodes.ALT);
+    event.ctrlKey = modifiers.includes(KeyCodes.CTRL);
+    event.metaKey = modifiers.includes(KeyCodes.META);
+    event.shiftKey = modifiers.includes(KeyCodes.SHIFT);
   }
   return new KeyboardEvent('keydown', event);
 }
diff --git a/tests/playgrounds/screenshot.js b/tests/playgrounds/screenshot.js
index af20f9d52..c443755a5 100644
--- a/tests/playgrounds/screenshot.js
+++ b/tests/playgrounds/screenshot.js
@@ -89,8 +89,7 @@ function workspaceToSvg_(workspace, callback, customCss) {
   const css = [].slice
     .call(document.head.querySelectorAll('style'))
     .filter(
-      (el) =>
-        /\.blocklySvg/.test(el.innerText) || el.id.indexOf('blockly-') === 0,
+      (el) => /\.blocklySvg/.test(el.innerText) || el.id.startsWith('blockly-'),
     )
     .map((el) => el.innerText)
     .join('\n');