diff --git a/packages/blob/src/index.js b/packages/blob/src/index.ts
similarity index 82%
rename from packages/blob/src/index.js
rename to packages/blob/src/index.ts
index 2493f81fc4c65..5f55d16c3f754 100644
--- a/packages/blob/src/index.js
+++ b/packages/blob/src/index.ts
@@ -1,7 +1,9 @@
+type BlobPart = BufferSource | Blob | string;
+
 /**
  * @type {Record<string, File|undefined>}
  */
-const cache = {};
+const cache: Record< string, File | undefined > = {};
 
 /**
  * Create a blob URL from a file.
@@ -10,7 +12,7 @@ const cache = {};
  *
  * @return {string} The blob URL.
  */
-export function createBlobURL( file ) {
+export function createBlobURL( file: File ): string {
 	const url = window.URL.createObjectURL( file );
 
 	cache[ url ] = file;
@@ -27,7 +29,7 @@ export function createBlobURL( file ) {
  *
  * @return {File|undefined} The file for the blob URL.
  */
-export function getBlobByURL( url ) {
+export function getBlobByURL( url: string ): File | undefined {
 	return cache[ url ];
 }
 
@@ -40,7 +42,7 @@ export function getBlobByURL( url ) {
  *
  * @return {string|undefined} The blob type.
  */
-export function getBlobTypeByURL( url ) {
+export function getBlobTypeByURL( url: string ): string | undefined {
 	return getBlobByURL( url )?.type.split( '/' )[ 0 ]; // 0: media type , 1: file extension eg ( type: 'image/jpeg' ).
 }
 
@@ -49,7 +51,7 @@ export function getBlobTypeByURL( url ) {
  *
  * @param {string} url The blob URL.
  */
-export function revokeBlobURL( url ) {
+export function revokeBlobURL( url: string ): void {
 	if ( cache[ url ] ) {
 		window.URL.revokeObjectURL( url );
 	}
@@ -64,7 +66,7 @@ export function revokeBlobURL( url ) {
  *
  * @return {boolean} Is the url a blob url?
  */
-export function isBlobURL( url ) {
+export function isBlobURL( url: string | undefined ): boolean {
 	if ( ! url || ! url.indexOf ) {
 		return false;
 	}
@@ -94,7 +96,11 @@ export function isBlobURL( url ) {
  * @param {BlobPart} content     File content (BufferSource | Blob | string).
  * @param {string}   contentType (Optional) File mime type. Default is `''`.
  */
-export function downloadBlob( filename, content, contentType = '' ) {
+export function downloadBlob(
+	filename: string,
+	content: BlobPart,
+	contentType: string = ''
+): void {
 	if ( ! filename || ! content ) {
 		return;
 	}
diff --git a/packages/blob/src/test/index.js b/packages/blob/src/test/index.ts
similarity index 85%
rename from packages/blob/src/test/index.js
rename to packages/blob/src/test/index.ts
index 47dcb5019ee25..04ba9700ce5b7 100644
--- a/packages/blob/src/test/index.js
+++ b/packages/blob/src/test/index.ts
@@ -1,7 +1,7 @@
 /**
  * Internal dependencies
  */
-import { isBlobURL, getBlobTypeByURL, downloadBlob } from '../';
+import { isBlobURL, getBlobTypeByURL, downloadBlob } from '..';
 
 describe( 'isBlobURL', () => {
 	it( 'returns true if the url starts with "blob:"', () => {
@@ -13,6 +13,8 @@ describe( 'isBlobURL', () => {
 	} );
 
 	it( 'returns false if the url is not defined', () => {
+		// calling isBlobURL without a URL is not type compliant, so ignore it
+		// @ts-ignore
 		expect( isBlobURL() ).toBe( false );
 	} );
 } );
@@ -23,6 +25,8 @@ describe( 'getBlobTypeByURL', () => {
 	} );
 
 	it( 'returns undefined if the url is not defined', () => {
+		// calling getBlobTypeByURL without a URL is not type compliant, so ignore it
+		// @ts-ignore
 		expect( getBlobTypeByURL() ).toBe( undefined );
 	} );
 } );
@@ -36,17 +40,18 @@ describe( 'downloadBlob', () => {
 	const createElementSpy = jest
 		.spyOn( global.document, 'createElement' )
 		.mockReturnValue( mockAnchorElement );
+
 	const mockBlob = jest.fn();
-	const blobSpy = jest.spyOn( window, 'Blob' ).mockReturnValue( mockBlob );
+	const blobSpy = jest
+		.spyOn( window, 'Blob' )
+		.mockReturnValue( mockBlob as unknown as Blob );
 	jest.spyOn( document.body, 'appendChild' );
 	jest.spyOn( document.body, 'removeChild' );
 	beforeEach( () => {
 		// Can't seem to spy on these static methods. They are `undefined`.
 		// Possibly overwritten: https://github.com/WordPress/gutenberg/blob/trunk/packages/jest-preset-default/scripts/setup-globals.js#L5
-		window.URL = {
-			createObjectURL,
-			revokeObjectURL,
-		};
+		window.URL.createObjectURL = createObjectURL;
+		window.URL.revokeObjectURL = revokeObjectURL;
 	} );
 
 	afterAll( () => {