diff --git a/src/AddThreepid.ts b/src/AddThreepid.ts
index 7e53bd79a2..34ba9d51ed 100644
--- a/src/AddThreepid.ts
+++ b/src/AddThreepid.ts
@@ -201,7 +201,7 @@ export default class AddThreepid {
                     // implemented it without, so this may just succeed and that's OK.
                     return [true];
                 } catch (err) {
-                    if (!(err instanceof MatrixError) || err.httpStatus !== 401 || !err.data || !err.data.flows) {
+                    if (!(err instanceof MatrixError) || err.httpStatus !== 401 || !err.data?.flows) {
                         // doesn't look like an interactive-auth failure
                         throw err;
                     }
@@ -300,7 +300,7 @@ export default class AddThreepid {
                 // implemented it without, so this may just succeed and that's OK.
                 return [true];
             } catch (err) {
-                if (!(err instanceof MatrixError) || err.httpStatus !== 401 || !err.data || !err.data.flows) {
+                if (!(err instanceof MatrixError) || err.httpStatus !== 401 || !err.data?.flows) {
                     // doesn't look like an interactive-auth failure
                     throw err;
                 }
diff --git a/src/Avatar.ts b/src/Avatar.ts
index 5821647ea8..a78aa4d03b 100644
--- a/src/Avatar.ts
+++ b/src/Avatar.ts
@@ -68,7 +68,7 @@ function isValidHexColor(color: string): boolean {
     return (
         typeof color === "string" &&
         (color.length === 7 || color.length === 9) &&
-        color.charAt(0) === "#" &&
+        color.startsWith("#") &&
         !color
             .slice(1)
             .split("")
diff --git a/src/ContentMessages.ts b/src/ContentMessages.ts
index 07c5491f51..b7f67321c1 100644
--- a/src/ContentMessages.ts
+++ b/src/ContentMessages.ts
@@ -396,11 +396,7 @@ export default class ContentMessages {
     }
 
     public getUploadLimit(): number | null {
-        if (this.mediaConfig !== null && this.mediaConfig["m.upload.size"] !== undefined) {
-            return this.mediaConfig["m.upload.size"];
-        } else {
-            return null;
-        }
+        return this.mediaConfig?.["m.upload.size"] ?? null;
     }
 
     public async sendContentListToRoom(
@@ -578,7 +574,7 @@ export default class ContentMessages {
                     logger.error(e);
                     content.msgtype = MsgType.File;
                 }
-            } else if (file.type.indexOf("audio/") === 0) {
+            } else if (file.type.startsWith("audio/")) {
                 content.msgtype = MsgType.Audio;
                 try {
                     const audioInfo = await infoForAudioFile(file);
@@ -588,7 +584,7 @@ export default class ContentMessages {
                     logger.error(e);
                     content.msgtype = MsgType.File;
                 }
-            } else if (file.type.indexOf("video/") === 0) {
+            } else if (file.type.startsWith("video/")) {
                 content.msgtype = MsgType.Video;
                 try {
                     const videoInfo = await infoForVideoFile(matrixClient, roomId, file);
@@ -648,11 +644,7 @@ export default class ContentMessages {
     }
 
     private isFileSizeAcceptable(file: File): boolean {
-        if (
-            this.mediaConfig !== null &&
-            this.mediaConfig["m.upload.size"] !== undefined &&
-            file.size > this.mediaConfig["m.upload.size"]
-        ) {
+        if (this.mediaConfig?.["m.upload.size"] !== undefined && file.size > this.mediaConfig["m.upload.size"]) {
             return false;
         }
         return true;
diff --git a/src/IdentityAuthClient.tsx b/src/IdentityAuthClient.tsx
index 3b78d9e570..8963b6bcf2 100644
--- a/src/IdentityAuthClient.tsx
+++ b/src/IdentityAuthClient.tsx
@@ -170,7 +170,7 @@ export default class IdentityAuthClient {
         // XXX: The spec is `token`, but we used `access_token` for a Sydent release.
         const { access_token: accessToken, token } =
             await this.identityClient.registerWithIdentityServer(hsOpenIdToken);
-        const identityAccessToken = token ? token : accessToken;
+        const identityAccessToken = token || accessToken;
         if (check) await this.checkToken(identityAccessToken);
         return identityAccessToken;
     }
diff --git a/src/Lifecycle.ts b/src/Lifecycle.ts
index 39d93dec11..89faa9e0e9 100644
--- a/src/Lifecycle.ts
+++ b/src/Lifecycle.ts
@@ -661,7 +661,7 @@ export async function setLoggedIn(credentials: IMatrixClientCreds): Promise<Matr
         logger.log("Pickle key not created");
     }
 
-    return doSetLoggedIn(Object.assign({}, credentials, { pickleKey }), true, true);
+    return doSetLoggedIn({ ...credentials, pickleKey: pickleKey ?? undefined }, true, true);
 }
 
 /**
diff --git a/src/NodeAnimator.tsx b/src/NodeAnimator.tsx
index eb1ce8cc47..bb6885e427 100644
--- a/src/NodeAnimator.tsx
+++ b/src/NodeAnimator.tsx
@@ -18,9 +18,6 @@ interface IProps {
     // either a list of child nodes, or a single child.
     children: React.ReactNode;
 
-    // optional transition information for changing existing children
-    transition?: object;
-
     // a list of state objects to apply to each child node in turn
     startStyles: React.CSSProperties[];
 
diff --git a/src/Notifier.ts b/src/Notifier.ts
index 23d239de0a..961d2171a8 100644
--- a/src/Notifier.ts
+++ b/src/Notifier.ts
@@ -71,7 +71,7 @@ type of tile.
 */
 const msgTypeHandlers: Record<string, (event: MatrixEvent) => string | null> = {
     [MsgType.KeyVerificationRequest]: (event: MatrixEvent) => {
-        const name = (event.sender || {}).name;
+        const name = event.sender?.name;
         return _t("notifier|m.key.verification.request", { name });
     },
     [M_LOCATION.name]: (event: MatrixEvent) => {
@@ -233,7 +233,7 @@ class NotifierClass extends TypedEventEmitter<keyof EmittedEvents, EmittedEvents
 
         // Play notification sound here
         const sound = this.getSoundForRoom(room.roomId);
-        logger.log(`Got sound ${(sound && sound.name) || "default"} for ${room.roomId}`);
+        logger.log(`Got sound ${sound?.name || "default"} for ${room.roomId}`);
 
         if (sound) {
             await this.backgroundAudio.play(sound.url);
diff --git a/src/PosthogAnalytics.ts b/src/PosthogAnalytics.ts
index 28e37282a5..2ffe8b8166 100644
--- a/src/PosthogAnalytics.ts
+++ b/src/PosthogAnalytics.ts
@@ -296,10 +296,10 @@ export class PosthogAnalytics {
                     // until the next time account data is refreshed and this function is called (most likely on next
                     // page load). This will happen pretty infrequently, so we can tolerate the possibility.
                     analyticsID = analyticsIdGenerator();
-                    await client.setAccountData(
-                        PosthogAnalytics.ANALYTICS_EVENT_TYPE,
-                        Object.assign({ id: analyticsID }, accountData),
-                    );
+                    await client.setAccountData(PosthogAnalytics.ANALYTICS_EVENT_TYPE, {
+                        id: analyticsID,
+                        ...accountData,
+                    });
                 }
                 if (this.posthog.get_distinct_id() === analyticsID) {
                     // No point identifying again
diff --git a/src/RoomInvite.tsx b/src/RoomInvite.tsx
index d4f156c91d..07a24dd384 100644
--- a/src/RoomInvite.tsx
+++ b/src/RoomInvite.tsx
@@ -35,14 +35,14 @@ export interface IInviteResult {
  * @param {function} progressCallback optional callback, fired after each invite.
  * @returns {Promise} Promise
  */
-export function inviteMultipleToRoom(
+export async function inviteMultipleToRoom(
     client: MatrixClient,
     roomId: string,
     addresses: string[],
     progressCallback?: () => void,
 ): Promise<IInviteResult> {
     const inviter = new MultiInviter(client, roomId, progressCallback);
-    return inviter.invite(addresses, undefined).then((states) => Promise.resolve({ states, inviter }));
+    return { states: await inviter.invite(addresses), inviter };
 }
 
 export function showStartChatInviteDialog(initialText = ""): void {
@@ -104,7 +104,7 @@ export function inviteUsersToRoom(
             logger.error(err.stack);
             Modal.createDialog(ErrorDialog, {
                 title: _t("invite|failed_title"),
-                description: err && err.message ? err.message : _t("invite|failed_generic"),
+                description: err?.message ?? _t("invite|failed_generic"),
             });
         });
 }
diff --git a/src/SlashCommands.tsx b/src/SlashCommands.tsx
index 02c2b33849..5fc4d8c357 100644
--- a/src/SlashCommands.tsx
+++ b/src/SlashCommands.tsx
@@ -450,7 +450,7 @@ export const Commands = [
                 const matches = args.match(/^(\S+)$/);
                 if (matches) {
                     let roomAlias = matches[1];
-                    if (roomAlias[0] !== "#") return reject(this.getUsage());
+                    if (!roomAlias.startsWith("#")) return reject(this.getUsage());
 
                     if (!roomAlias.includes(":")) {
                         roomAlias += ":" + cli.getDomain();
@@ -994,7 +994,7 @@ Commands.forEach((cmd) => {
 export function parseCommandString(input: string): { cmd?: string; args?: string } {
     // trim any trailing whitespace, as it can confuse the parser for IRC-style commands
     input = input.trimEnd();
-    if (input[0] !== "/") return {}; // not a command
+    if (!input.startsWith("/")) return {}; // not a command
 
     const bits = input.match(/^(\S+?)(?:[ \n]+((.|\n)*))?$/);
     let cmd: string;
diff --git a/src/SlidingSyncManager.ts b/src/SlidingSyncManager.ts
index eeac10b603..e3ca77f988 100644
--- a/src/SlidingSyncManager.ts
+++ b/src/SlidingSyncManager.ts
@@ -72,27 +72,23 @@ const DEFAULT_ROOM_SUBSCRIPTION_INFO = {
 };
 // lazy load room members so rooms like Matrix HQ don't take forever to load
 const UNENCRYPTED_SUBSCRIPTION_NAME = "unencrypted";
-const UNENCRYPTED_SUBSCRIPTION = Object.assign(
-    {
-        required_state: [
-            [MSC3575_WILDCARD, MSC3575_WILDCARD], // all events
-            [EventType.RoomMember, MSC3575_STATE_KEY_ME], // except for m.room.members, get our own membership
-            [EventType.RoomMember, MSC3575_STATE_KEY_LAZY], // ...and lazy load the rest.
-        ],
-    },
-    DEFAULT_ROOM_SUBSCRIPTION_INFO,
-);
+const UNENCRYPTED_SUBSCRIPTION = {
+    required_state: [
+        [MSC3575_WILDCARD, MSC3575_WILDCARD], // all events
+        [EventType.RoomMember, MSC3575_STATE_KEY_ME], // except for m.room.members, get our own membership
+        [EventType.RoomMember, MSC3575_STATE_KEY_LAZY], // ...and lazy load the rest.
+    ],
+    ...DEFAULT_ROOM_SUBSCRIPTION_INFO,
+};
 
 // we need all the room members in encrypted rooms because we need to know which users to encrypt
 // messages for.
-const ENCRYPTED_SUBSCRIPTION = Object.assign(
-    {
-        required_state: [
-            [MSC3575_WILDCARD, MSC3575_WILDCARD], // all events
-        ],
-    },
-    DEFAULT_ROOM_SUBSCRIPTION_INFO,
-);
+const ENCRYPTED_SUBSCRIPTION = {
+    required_state: [
+        [MSC3575_WILDCARD, MSC3575_WILDCARD], // all events
+    ],
+    ...DEFAULT_ROOM_SUBSCRIPTION_INFO,
+};
 
 export type PartialSlidingSyncRequest = {
     filters?: MSC3575Filter;
@@ -199,10 +195,10 @@ export class SlidingSyncManager {
                         [EventType.RoomMember, MSC3575_STATE_KEY_ME], // lets the client calculate that we are in fact in the room
                     ],
                 },
+                ...updateArgs,
             };
-            list = Object.assign(list, updateArgs);
         } else {
-            const updatedList = Object.assign({}, list, updateArgs);
+            const updatedList = { ...list, ...updateArgs };
             // cannot use objectHasDiff as we need to do deep diff checking
             if (JSON.stringify(list) === JSON.stringify(updatedList)) {
                 logger.debug("list matches, not sending, update => ", updateArgs);
diff --git a/src/Terms.ts b/src/Terms.ts
index ee5ddfd854..868e2428c6 100644
--- a/src/Terms.ts
+++ b/src/Terms.ts
@@ -102,13 +102,8 @@ export async function startTermsFlow(
     });
 
     // fetch the set of agreed policy URLs from account data
-    const currentAcceptedTerms = await client.getAccountData("m.accepted_terms");
-    let agreedUrlSet: Set<string>;
-    if (!currentAcceptedTerms || !currentAcceptedTerms.getContent() || !currentAcceptedTerms.getContent().accepted) {
-        agreedUrlSet = new Set();
-    } else {
-        agreedUrlSet = new Set(currentAcceptedTerms.getContent().accepted);
-    }
+    const currentAcceptedTerms = client.getAccountData("m.accepted_terms")?.getContent();
+    const agreedUrlSet = new Set<string>(currentAcceptedTerms?.accepted || []);
 
     // remove any policies the user has already agreed to and any services where
     // they've already agreed to all the policies
diff --git a/src/actions/RoomListActions.ts b/src/actions/RoomListActions.ts
index 1b693ba4dd..578226986d 100644
--- a/src/actions/RoomListActions.ts
+++ b/src/actions/RoomListActions.ts
@@ -79,7 +79,7 @@ export default class RoomListActions {
                         logger.error("Failed to set DM tag " + err);
                         Modal.createDialog(ErrorDialog, {
                             title: _t("room_list|failed_set_dm_tag"),
-                            description: err && err.message ? err.message : _t("invite|failed_generic"),
+                            description: err?.message ?? _t("invite|failed_generic"),
                         });
                     });
                 }
@@ -95,7 +95,7 @@ export default class RoomListActions {
                         logger.error("Failed to remove tag " + oldTag + " from room: " + err);
                         Modal.createDialog(ErrorDialog, {
                             title: _t("room_list|failed_remove_tag", { tagName: oldTag }),
-                            description: err && err.message ? err.message : _t("invite|failed_generic"),
+                            description: err?.message ?? _t("invite|failed_generic"),
                         });
                     });
 
@@ -108,7 +108,7 @@ export default class RoomListActions {
                         logger.error("Failed to add tag " + newTag + " to room: " + err);
                         Modal.createDialog(ErrorDialog, {
                             title: _t("room_list|failed_add_tag", { tagName: newTag }),
-                            description: err && err.message ? err.message : _t("invite|failed_generic"),
+                            description: err?.message ?? _t("invite|failed_generic"),
                         });
 
                         throw err;
diff --git a/src/components/structures/MatrixChat.tsx b/src/components/structures/MatrixChat.tsx
index 0d7251c864..b6c9d890cb 100644
--- a/src/components/structures/MatrixChat.tsx
+++ b/src/components/structures/MatrixChat.tsx
@@ -1317,7 +1317,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                 const errCode = err.errcode || _td("error|unknown_error_code");
                 Modal.createDialog(ErrorDialog, {
                     title: _t("error_dialog|forget_room_failed", { errCode }),
-                    description: err && err.message ? err.message : _t("invite|failed_generic"),
+                    description: err?.message ?? _t("invite|failed_generic"),
                 });
             });
     }
diff --git a/src/components/views/dialogs/RoomUpgradeDialog.tsx b/src/components/views/dialogs/RoomUpgradeDialog.tsx
index 0935fca19f..337c1a334c 100644
--- a/src/components/views/dialogs/RoomUpgradeDialog.tsx
+++ b/src/components/views/dialogs/RoomUpgradeDialog.tsx
@@ -52,8 +52,7 @@ export default class RoomUpgradeDialog extends React.Component<IProps, IState> {
             .catch((err) => {
                 Modal.createDialog(ErrorDialog, {
                     title: _t("room_settings|advanced|error_upgrade_title"),
-                    description:
-                        err && err.message ? err.message : _t("room_settings|advanced|error_upgrade_description"),
+                    description: err?.message ?? _t("room_settings|advanced|error_upgrade_description"),
                 });
             })
             .finally(() => {
diff --git a/src/components/views/right_panel/UserInfo.tsx b/src/components/views/right_panel/UserInfo.tsx
index bb03066b88..d6f4b0300a 100644
--- a/src/components/views/right_panel/UserInfo.tsx
+++ b/src/components/views/right_panel/UserInfo.tsx
@@ -725,7 +725,7 @@ export const RoomKickButton = ({
                     logger.error("Kick error: " + err);
                     Modal.createDialog(ErrorDialog, {
                         title: _t("user_info|error_kicking_user"),
-                        description: err && err.message ? err.message : "Operation failed",
+                        description: err?.message ?? "Operation failed",
                     });
                 },
             )
diff --git a/src/components/views/settings/AddRemoveThreepids.tsx b/src/components/views/settings/AddRemoveThreepids.tsx
index 4535400c33..8b2b61bb9a 100644
--- a/src/components/views/settings/AddRemoveThreepids.tsx
+++ b/src/components/views/settings/AddRemoveThreepids.tsx
@@ -74,7 +74,7 @@ const ExistingThreepid: React.FC<ExistingThreepidProps> = ({ mode, threepid, onC
                     logger.error("Unable to remove contact information: " + err);
                     Modal.createDialog(ErrorDialog, {
                         title: _t("settings|general|error_remove_3pid"),
-                        description: err && err.message ? err.message : _t("invite|failed_generic"),
+                        description: err?.message ?? _t("invite|failed_generic"),
                     });
                 });
         },
diff --git a/test/unit-tests/Lifecycle-test.ts b/test/unit-tests/Lifecycle-test.ts
index 19bf93cdd6..67ac7c7637 100644
--- a/test/unit-tests/Lifecycle-test.ts
+++ b/test/unit-tests/Lifecycle-test.ts
@@ -630,7 +630,7 @@ describe("Lifecycle", () => {
                         deviceId,
                         freshLogin: true,
                         guest: false,
-                        pickleKey: null,
+                        pickleKey: undefined,
                     },
                     undefined,
                 );