diff --git a/src/camera/core-impl.ts b/src/camera/core-impl.ts
index ad29ec45..7109174e 100644
--- a/src/camera/core-impl.ts
+++ b/src/camera/core-impl.ts
@@ -218,11 +218,12 @@ class RenderedCameraImpl implements RenderedCamera {
     private getFirstTrackOrFail(): MediaStreamTrack {
         this.failIfClosed();
 
-        if (this.mediaStream.getVideoTracks().length === 0) {
+        const firstTrack = this.mediaStream.getVideoTracks()[0];
+        if (!firstTrack) {
             throw "No video tracks found";
-        }
 
-        return this.mediaStream.getVideoTracks()[0];
+        }
+        return firstTrack;
     }
 
     //#region Public APIs.
diff --git a/src/core.ts b/src/core.ts
index 8d3d9656..7e14dd2e 100644
--- a/src/core.ts
+++ b/src/core.ts
@@ -89,7 +89,7 @@ export class Html5QrcodeConstants {
     static DEFAULT_REMEMBER_LAST_CAMERA_USED = true;
     static DEFAULT_SUPPORTED_SCAN_TYPE = [
         Html5QrcodeScanType.SCAN_TYPE_CAMERA,
-        Html5QrcodeScanType.SCAN_TYPE_FILE];
+        Html5QrcodeScanType.SCAN_TYPE_FILE] as const;
 }
 
 /** Defines dimension for QR Code Scanner. */
diff --git a/src/html5-qrcode-scanner.ts b/src/html5-qrcode-scanner.ts
index 028262fe..a29bc48d 100644
--- a/src/html5-qrcode-scanner.ts
+++ b/src/html5-qrcode-scanner.ts
@@ -114,7 +114,7 @@ export interface Html5QrcodeScannerConfig
      *    - [SCAN_TYPE_FILE] - Only file based scan supported.
      *  - Setting wrong values or multiple values will fail.
      */
-    supportedScanTypes?: Array<Html5QrcodeScanType> | [];
+    supportedScanTypes?: ReadonlyArray<Html5QrcodeScanType> | [];
 
     /**
      * If `true` the rendered UI will have button to turn flash on or off
diff --git a/src/html5-qrcode.ts b/src/html5-qrcode.ts
index b3fcbdab..ec05fc43 100644
--- a/src/html5-qrcode.ts
+++ b/src/html5-qrcode.ts
@@ -1259,12 +1259,12 @@ export class Html5Qrcode {
             };
 
             const keys = Object.keys(cameraIdOrConfig);
-            if (keys.length !== 1) {
+            const key = keys[0];
+            if (!key) {
                 throw "'cameraIdOrConfig' object should have exactly 1 key,"
                     + ` if passed as an object, found ${keys.length} keys`;
             }
 
-            const key:string = Object.keys(cameraIdOrConfig)[0];
             if (key !== facingModeKey && key !== deviceIdKey) {
                 throw `Only '${facingModeKey}' and '${deviceIdKey}' `
                     + " are supported for 'cameraIdOrConfig'";
diff --git a/src/ui/scanner/file-selection-ui.ts b/src/ui/scanner/file-selection-ui.ts
index ebf68f72..91186779 100644
--- a/src/ui/scanner/file-selection-ui.ts
+++ b/src/ui/scanner/file-selection-ui.ts
@@ -69,11 +69,10 @@ export class FileSelectionUi {
                 return;
             }
             let target: HTMLInputElement = e.target as HTMLInputElement;
-            if (target.files && target.files.length === 0) {
+            const file = target.files?.[0];
+            if (!file) {
                 return;
             }
-            let fileList: FileList = target.files!;
-            const file: File = fileList[0];
             let fileName = file.name;
             $this.setImageNameToButton(fileName);
 
diff --git a/src/ui/scanner/scan-type-selector.ts b/src/ui/scanner/scan-type-selector.ts
index d822e160..f7fd8874 100644
--- a/src/ui/scanner/scan-type-selector.ts
+++ b/src/ui/scanner/scan-type-selector.ts
@@ -15,9 +15,9 @@ import {
 
 /** Util class to help with scan type selection in scanner class. */
 export class ScanTypeSelector {
-    private supportedScanTypes: Array<Html5QrcodeScanType>;
+    private supportedScanTypes: readonly [Html5QrcodeScanType, ...Array<Html5QrcodeScanType>];
 
-    constructor(supportedScanTypes?: Array<Html5QrcodeScanType> | []) {
+    constructor(supportedScanTypes?: ReadonlyArray<Html5QrcodeScanType> | []) {
         this.supportedScanTypes = this.validateAndReturnScanTypes(
             supportedScanTypes);
     }
@@ -65,8 +65,8 @@ export class ScanTypeSelector {
      * Fails early if the config values is incorrectly set.
      */
     private validateAndReturnScanTypes(
-        supportedScanTypes?:Array<Html5QrcodeScanType>):
-        Array<Html5QrcodeScanType> {
+        supportedScanTypes?:ReadonlyArray<Html5QrcodeScanType>):
+        readonly [Html5QrcodeScanType, ...Array<Html5QrcodeScanType>] {
         // If not set, use the default values and order.
         if (!supportedScanTypes || supportedScanTypes.length === 0) {
             return Html5QrcodeConstants.DEFAULT_SUPPORTED_SCAN_TYPE;
@@ -88,7 +88,7 @@ export class ScanTypeSelector {
             }
         }
 
-        return supportedScanTypes;
+        return supportedScanTypes as [Html5QrcodeScanType, ...Array<Html5QrcodeScanType>];
     }
     //#endregion
 }
diff --git a/tests/ui/scanner/camera-selection-ui.test.ts b/tests/ui/scanner/camera-selection-ui.test.ts
index 22896185..428b13e8 100644
--- a/tests/ui/scanner/camera-selection-ui.test.ts
+++ b/tests/ui/scanner/camera-selection-ui.test.ts
@@ -123,10 +123,10 @@ describe("CameraSelectionUi setting and getting values", () => {
         let cameraSelectUi = CameraSelectionUi.create(parentElement!, cameras);
 
         // First camera is default.
-        expect(cameraSelectUi.getValue()).eq(cameras[0].id);
+        expect(cameraSelectUi.getValue()).eq(cameras[0]!.id);
 
-        cameraSelectUi.setValue(cameras[1].id);
-        expect(cameraSelectUi.getValue()).eq(cameras[1].id);
+        cameraSelectUi.setValue(cameras[1]!.id);
+        expect(cameraSelectUi.getValue()).eq(cameras[1]!.id);
 
         expect(() => {
             cameraSelectUi.setValue("random string");
@@ -138,7 +138,7 @@ describe("CameraSelectionUi setting and getting values", () => {
         let cameras = createCameraList(numCameras);
         let cameraSelectUi = CameraSelectionUi.create(parentElement!, cameras);
 
-        expect(cameraSelectUi.hasValue(cameras[1].id)).to.be.true;
+        expect(cameraSelectUi.hasValue(cameras[1]!.id)).to.be.true;
         expect(cameraSelectUi.hasValue("random string")).to.be.false;
     });
 });
diff --git a/tsconfig.json b/tsconfig.json
index 67e237ab..092f0182 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -11,6 +11,7 @@
         // Flags to ensure code quality.
         "strict": true,
         "noImplicitReturns": true,
+        "noUncheckedIndexedAccess": true,
         "noUnusedParameters": true,
         "experimentalDecorators": true,
         "removeComments": true,