chore(compartment-mapper): strongly type a function for lulz

packages/compartment-mapper/src/policy.js

@@ -29,18 +29,24 @@ export const ATTENUATORS_COMPARTMENT = '<ATTENUATORS>';
 
 /**
  * Copies properties (optionally limited to a specific list) from one object to another.
- *
- * @param {object} from
- * @param {object} to
- * @param {Array<string | symbol>} [list]
- * @returns {object}
+ * @template {Record<PropertyKey, any>} T
+ * @template {Record<PropertyKey, any>} U
+ * @template {Array<Partial<keyof T>>} [K=Array<keyof T>]
+ * @param {T} from
+ * @param {U} to
+ * @param {K} [list]
+ * @returns {Omit<U, K[number]> & Pick<T, K[number]>}
  */
 const selectiveCopy = (from, to, list) => {
+  /** @type {Array<Partial<keyof T>>} */
+  let props;
   if (!list) {
-    list = keys(from);
+    props = /** @type {Array<keyof T>} */ (keys(from));
+  } else {
+    props = list;
   }
-  for (let index = 0; index < list.length; index += 1) {
-    const key = list[index];
+  for (let index = 0; index < props.length; index += 1) {
+    const key = props[index];
     // If an endowment is missing, global value is undefined.
     // This is an expected behavior if globals are used for platform feature detection
     to[key] = from[key];