diff --git a/src/helpers.js b/src/helpers.ts
similarity index 59%
rename from src/helpers.js
rename to src/helpers.ts
index 03f1399..d82958a 100644
--- a/src/helpers.js
+++ b/src/helpers.ts
@@ -1,15 +1,26 @@
-const { spawnSync } = require('child_process')
-const { readFileSync, writeFileSync } = require('fs')
+import { spawnSync } from 'child_process'
+import { readFileSync, writeFileSync } from 'fs'
 
 const PACKAGE_SIZE_PATT = /package size:\s+([0-9]+\.?[0-9]*\s+[A-Za-z]+)/g
 const UNPACKED_SIZE_PATT = /unpacked size:\s+([0-9]+\.?[0-9]*\s+[A-Za-z]+)/g
 const SIZE_SUFFIX_PATT = /([A-Za-z]+)/
 const SIZE_MAGNITUDE_PATT = /([0-9]+\.?[0-9]*)/
-const MANIFEST_FILENAME = '.packwatch.json'
 
-const FS_OPTIONS = { encoding: 'utf-8' }
+export const MANIFEST_FILENAME = '.packwatch.json'
 
-function convertSizeToBytes(sizeString) {
+type Report = {
+    packageSize: string
+    unpackedSize: string
+    packageSizeBytes?: number
+    unpackedSizeBytes?: number
+}
+
+type Digest = {
+    limit: string
+    packageSize: string
+}
+
+export function convertSizeToBytes(sizeString: string): number {
     const sizeSuffix = SIZE_SUFFIX_PATT.exec(sizeString)[1]
     const sizeMagnitude = SIZE_MAGNITUDE_PATT.exec(sizeString)[1]
 
@@ -23,10 +34,13 @@ function convertSizeToBytes(sizeString) {
     return multiplier * parseFloat(sizeMagnitude)
 }
 
-function getCurrentPackageStats() {
-    const { stderr } = spawnSync('npm', ['pack', '--dry-run'], FS_OPTIONS)
-    const packageSize = PACKAGE_SIZE_PATT.exec(stderr)[1]
-    const unpackedSize = UNPACKED_SIZE_PATT.exec(stderr)[1]
+export function getCurrentPackageStats(): Report {
+    const { stderr } = spawnSync('npm', ['pack', '--dry-run'], {
+        encoding: 'utf-8',
+    })
+    const stderrString = String(stderr)
+    const packageSize = PACKAGE_SIZE_PATT.exec(stderrString)[1]
+    const unpackedSize = UNPACKED_SIZE_PATT.exec(stderrString)[1]
 
     return {
         packageSize,
@@ -36,9 +50,11 @@ function getCurrentPackageStats() {
     }
 }
 
-function getPreviousPackageStats() {
+export function getPreviousPackageStats(): Report | null {
     try {
-        const currentManifest = readFileSync(MANIFEST_FILENAME, FS_OPTIONS)
+        const currentManifest = readFileSync(MANIFEST_FILENAME, {
+            encoding: 'utf-8',
+        })
         const parsedManifest = JSON.parse(currentManifest)
         return {
             ...parsedManifest,
@@ -46,12 +62,20 @@ function getPreviousPackageStats() {
             unpackedSizeBytes: convertSizeToBytes(parsedManifest.unpackedSize),
             limitBytes: convertSizeToBytes(parsedManifest.limit),
         }
-    } catch (e) {
-        return {}
+    } catch {
+        /* No manifest */
     }
 }
 
-function createOrUpdateManifest({ previous, current, updateLimit = false }) {
+export function createOrUpdateManifest({
+    previous,
+    current,
+    updateLimit = false,
+}: {
+    previous?: Digest
+    current: Report
+    updateLimit?: boolean
+}) {
     const { limit } = previous || {}
     const { packageSize, unpackedSize } = current
 
@@ -63,11 +87,3 @@ function createOrUpdateManifest({ previous, current, updateLimit = false }) {
 
     writeFileSync(MANIFEST_FILENAME, JSON.stringify(newManifest))
 }
-
-module.exports = {
-    createOrUpdateManifest,
-    getPreviousPackageStats,
-    getCurrentPackageStats,
-    convertSizeToBytes,
-    MANIFEST_FILENAME,
-}
diff --git a/src/index.test.js b/src/index.test.ts
similarity index 94%
rename from src/index.test.js
rename to src/index.test.ts
index ae0a9aa..a178827 100644
--- a/src/index.test.js
+++ b/src/index.test.ts
@@ -1,18 +1,19 @@
-const childProcess = require('child_process')
-const { readFileSync } = require('fs')
+import * as childProcess from 'child_process'
+import { readFileSync } from 'fs'
 
-const mockFS = require('mock-fs')
+import mockFS from 'mock-fs'
 
-jest.mock('child_process')
-childProcess.spawnSync = jest.fn(() => ({ stderr: mockPackOutput }))
+jest.mock('child_process', () => ({
+    spawnSync: () => ({ stderr: mockPackOutput })
+}))
 
-const {
+import {
     MANIFEST_FILENAME,
     convertSizeToBytes,
+    createOrUpdateManifest,
     getCurrentPackageStats,
     getPreviousPackageStats,
-    createOrUpdateManifest,
-} = require('./helpers')
+} from './helpers'
 
 const mockPackageSize = '1.1 kB'
 const mockUnpackedSize = '9000 kB'
@@ -100,7 +101,7 @@ describe('Helpers', () => {
                 [MANIFEST_FILENAME]: 'not valid JSON',
             })
 
-            expect(getPreviousPackageStats()).toEqual({})
+            expect(getPreviousPackageStats()).toBeUndefined()
         })
     })
 
diff --git a/src/index.js b/src/index.ts
similarity index 100%
rename from src/index.js
rename to src/index.ts