diff --git a/frontend/jsconfig.json b/frontend/jsconfig.json
index 9660d5f..9114199 100644
--- a/frontend/jsconfig.json
+++ b/frontend/jsconfig.json
@@ -22,6 +22,7 @@
   "include": [
     "src/**/*.d.ts",
     "src/**/*.js",
+    "src/**/*.ts",
     "src/**/*.svelte"
   ]
 }
diff --git a/frontend/src/lib/actions/input.js b/frontend/src/lib/actions/input.js
index 369dd17..fea6f19 100644
--- a/frontend/src/lib/actions/input.js
+++ b/frontend/src/lib/actions/input.js
@@ -14,7 +14,7 @@ export default function input(node, { autofocus, type, onValid, onInvalid, manda
   node.setAttribute('autocomplete', false);
 
   const getMessage = () => {
-    const checkInteger = () => (isInt(node.value) ? false : 'Value must be an integer');
+    const checkInteger = () => (Number.isInteger(node.value) ? false : 'Value must be an integer');
     const checkNumberBoundaries = boundaries => {
       if (node.value < boundaries[0]) {
         return `Input is too low for type ${type}`;
diff --git a/frontend/src/lib/constants.js b/frontend/src/lib/constants.js
deleted file mode 100644
index b6d1d9b..0000000
--- a/frontend/src/lib/constants.js
+++ /dev/null
@@ -1,7 +0,0 @@
-// Months
-export const months = [ 'January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December' ];
-export const monthsAbbr = months.map(m => m.slice(0, 3));
-
-// Days
-export const days = [ 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday' ];
-export const daysAbbr = days.map(d => d.slice(0, 3));
diff --git a/frontend/src/lib/constants.ts b/frontend/src/lib/constants.ts
new file mode 100644
index 0000000..7aa0a38
--- /dev/null
+++ b/frontend/src/lib/constants.ts
@@ -0,0 +1,27 @@
+export const months = [
+  'January',
+  'February',
+  'March',
+  'April',
+  'May',
+  'June',
+  'July',
+  'August',
+  'September',
+  'October',
+  'November',
+  'December'
+];
+
+export const days = [
+  'Monday',
+  'Tuesday',
+  'Wednesday',
+  'Thursday',
+  'Friday',
+  'Saturday',
+  'Sunday'
+];
+
+export const daysAbbr = days.map(d => d.slice(0, 3));
+export const monthsAbbr = months.map(m => m.slice(0, 3));
diff --git a/frontend/src/lib/math.js b/frontend/src/lib/math.ts
similarity index 58%
rename from frontend/src/lib/math.js
rename to frontend/src/lib/math.ts
index c76ca77..22be3f0 100644
--- a/frontend/src/lib/math.js
+++ b/frontend/src/lib/math.ts
@@ -1,13 +1,4 @@
-// https://stackoverflow.com/a/14794066
-export function isInt(value) {
-  if (isNaN(value)) {
-    return false;
-  }
-  const x = parseFloat(value);
-  return (x | 0) === x;
-}
-
-export function randInt(min, max) {
+export function randInt(min: number, max: number) {
   return Math.round(Math.random() * (max - min) + min);
 }
 
diff --git a/frontend/src/lib/strings.js b/frontend/src/lib/strings.ts
similarity index 50%
rename from frontend/src/lib/strings.js
rename to frontend/src/lib/strings.ts
index cc06f29..cf9ade2 100644
--- a/frontend/src/lib/strings.js
+++ b/frontend/src/lib/strings.ts
@@ -1,19 +1,19 @@
-export function capitalise(string = '') {
+export function capitalise(string = ''): string {
   const capitalised = string.charAt(0).toUpperCase() + string.slice(1);
   return capitalised;
 }
 
-export function jsonLooseParse(json) {
-  const obj = new Function(`return (${json})`)();
+export function jsonLooseParse<T>(json: string): T {
+  const obj: T = new Function(`return (${json})`)();
   return obj;
 }
 
-export function convertLooseJson(json) {
+export function convertLooseJson(json: any) {
   const j = JSON.stringify(jsonLooseParse(json));
   return j;
 }
 
-export function looseJsonIsValid(json) {
+export function looseJsonIsValid(json: string): boolean {
   try {
     jsonLooseParse(json);
     return true;
@@ -23,6 +23,6 @@ export function looseJsonIsValid(json) {
   }
 }
 
-export function stringCouldBeID(string) {
+export function stringCouldBeID(string: string) {
   return /^[a-zA-Z0-9_-]{1,}$/.test(string);
 }