diff --git a/app/src/helpers/commons.ts b/app/src/helpers/commons.ts
index 421aee72..abe4cc55 100644
--- a/app/src/helpers/commons.ts
+++ b/app/src/helpers/commons.ts
@@ -1,13 +1,19 @@
+import type { UnwrapRef } from 'vue'
+
+import type { Obj } from '@/types/commons'
+
 /**
  * Allow to set a timeout on a `Promise` expected response.
  * The returned Promise will be rejected if the original Promise is not resolved or
  * rejected before the delay.
  *
- * @param {Promise} promise - A promise (like a fetch call).
- * @param {Number} delay - delay after which the promise is rejected
- * @return {Promise}
+ * @param promise - A promise (like a fetch call).
+ * @param delay - delay after which the promise is rejected
  */
-export function timeout(promise, delay) {
+export function timeout<T extends unknown>(
+  promise: Promise<T>,
+  delay: number,
+): Promise<T> {
   return new Promise((resolve, reject) => {
     // FIXME reject(new Error('api_not_responding')) for post-install
     setTimeout(() => reject, delay)
@@ -18,10 +24,9 @@ export function timeout(promise, delay) {
 /**
  * Check if passed value is an object literal.
  *
- * @param {*} value - Anything.
- * @return {Boolean}
+ * @param value - Anything.
  */
-export function isObjectLiteral(value) {
+export function isObjectLiteral(value: any): value is object {
   return (
     value !== null &&
     value !== undefined &&
@@ -41,23 +46,52 @@ export function objectGet<
  * Check if value is "empty" (`null`, `undefined`, `''`, `[]`, '{}').
  * Note: `0` is not considered "empty" in that helper.
  *
- * @param {*} value - Anything.
- * @return {Boolean}
+ * @param value - Anything.
  */
-export function isEmptyValue(value) {
-  if (typeof value === 'number') return false
-  return !value || value.length === 0 || Object.keys(value).length === 0
+export function isEmptyValue(
+  value: any,
+): value is null | undefined | '' | [] | {} {
+  if (typeof value === 'number' || typeof value === 'boolean') return false
+  return (
+    !value ||
+    (Array.isArray(value) && value.length === 0) ||
+    Object.keys(value).length === 0
+  )
 }
 
+type Flatten<T extends object> = object extends T
+  ? object
+  : {
+        [K in keyof T]-?: (
+          x: NonNullable<T[K]> extends infer V
+            ? V extends object
+              ? V extends readonly any[]
+                ? Pick<T, K>
+                : Flatten<V> extends infer FV
+                  ? {
+                      [P in keyof FV as `${Extract<P, string | number>}`]: FV[P]
+                    }
+                  : never
+              : Pick<T, K>
+            : never,
+        ) => void
+      } extends Record<keyof T, (y: infer O) => void>
+    ? O extends infer U
+      ? { [K in keyof O]: O[K] }
+      : never
+    : never
+
 /**
  * Returns an flattened object literal, with all keys at first level and removing nested ones.
  *
- * @param {Object} obj - An object literal to flatten.
- * @param {Object} [flattened={}] - An object literal to add passed obj keys/values.
- * @return {Object}
+ * @param obj - An object literal to flatten.
+ * @param flattened - An object literal to add passed obj keys/values.
  */
-export function flattenObjectLiteral(obj, flattened = {}) {
-  function flatten(objLit) {
+export function flattenObjectLiteral<T extends object>(
+  obj: T,
+  flattened: Partial<Flatten<T>> = {},
+) {
+  function flatten(objLit: Partial<Flatten<T>>) {
     for (const key in objLit) {
       const value = objLit[key]
       if (isObjectLiteral(value)) {
@@ -68,18 +102,24 @@ export function flattenObjectLiteral(obj, flattened = {}) {
     }
   }
   flatten(obj)
-  return flattened
+  return flattened as Flatten<T>
 }
 
 /**
  * Returns an new Object filtered with passed filter function.
  * Each entry `[key, value]` will be forwarded to the `filter` function.
  *
- * @param {Object} obj - object to filter.
- * @param {Function} filter - the filter function to call for each entry.
- * @return {Object}
+ * @param obj - object to filter.
+ * @param filter - the filter function to call for each entry.
  */
-export function filterObject(obj, filter) {
+export function filterObject<T extends Obj>(
+  obj: T,
+  filter: (
+    entries: [string, any],
+    index: number,
+    array: [string, any][],
+  ) => boolean,
+) {
   return Object.fromEntries(
     Object.entries(obj).filter((...args) => filter(...args)),
   )
@@ -87,22 +127,20 @@ export function filterObject(obj, filter) {
 
 /**
  * Returns an new array containing items that are in first array but not in the other.
- *
- * @param {Array} [arr1=[]]
- * @param {Array} [arr2=[]]
- * @return {Array}
  */
-export function arrayDiff(arr1 = [], arr2 = []) {
+export function arrayDiff<T extends string>(
+  arr1: T[] = [],
+  arr2: T[] = [],
+): T[] {
   return arr1.filter((item) => !arr2.includes(item))
 }
 
 /**
  * Returns a new string with escaped HTML (`&<>"'` replaced by entities).
  *
- * @param {String} unsafe
- * @return {String}
+ * @param unsafe - string to escape
  */
-export function escapeHtml(unsafe) {
+export function escapeHtml(unsafe: string) {
   return unsafe
     .replace(/&/g, '&amp;')
     .replace(/</g, '&lt;')
@@ -114,11 +152,10 @@ export function escapeHtml(unsafe) {
 /**
  * Returns a random integer between `min` and `max`.
  *
- * @param {Number} min
- * @param {Number} max
- * @return {Number}
+ * @param min - min possible value
+ * @param max - max possible value
  */
-export function randint(min, max) {
+export function randint(min: number, max: number) {
   return Math.floor(Math.random() * (max - min + 1)) + min
 }