Typed object from entries (#53)

Author: jossmac

.changeset/smooth-news-deliver.md

@@ -0,0 +1,5 @@
+---
+'emery': patch
+---
+
+Add `typedObjectFromEntries` utility, and improve `ObjectEntry` type.

src/index.ts

@@ -34,7 +34,7 @@ export {
 export { castToOpaque } from './opaques';
 
 export { getErrorMessage } from './utils/error';
-export { typedEntries, typedKeys } from './utils/object';
+export { typedEntries, typedKeys, typedObjectFromEntries } from './utils/object';
 
 // Types
 // ------------------------------

src/types.ts

@@ -5,7 +5,7 @@
 
 export type ErrorLike = { message: string };
 
-export type ObjectEntry<T> = { [K in keyof T]: [K, T[K]] }[keyof T];
+export type ObjectEntry<T> = { [K in keyof T]-?: [K, T[K]] }[keyof T];
 
 export type Nullish = null | undefined;
 

src/utils/object.test.ts

@@ -1,4 +1,4 @@
-import { typedEntries, typedKeys } from './object';
+import { typedEntries, typedKeys, typedObjectFromEntries } from './object';
 
 describe('utils/object', () => {
   describe('typedEntries', () => {
@@ -16,4 +16,13 @@ describe('utils/object', () => {
       expect(result).toEqual(['foo', 'bar']);
     });
   });
+  describe('typedObjectFromEntries', () => {
+    it('should return the correct object', () => {
+      const result = typedObjectFromEntries([
+        ['foo', 1],
+        ['bar', 2],
+      ]);
+      expect(result).toEqual({ foo: 1, bar: 2 });
+    });
+  });
 });

src/utils/object.ts

@@ -21,3 +21,18 @@ export function typedEntries<T extends object>(value: T) {
 export function typedKeys<T extends object>(value: T) {
   return Object.keys(value) as Array<keyof T>;
 }
+
+/**
+ * An alternative to `Object.fromEntries()` that avoids type widening. Must be
+ * used in conjunction with `typedEntries` or `typedKeys`.
+ *
+ * @example
+ * const obj = { name: 'Alice', age: 30 };
+ * const rebuilt1 = Object.fromEntries(Object.entries(obj));
+ * //    ^? { [k: string]: string | number }
+ * const rebuilt2 = typedObjectFromEntries(typedEntries(obj));
+ * //    ^? { name: string, age: number }
+ */
+export function typedObjectFromEntries<T extends object>(entries: ObjectEntry<T>[]) {
+  return Object.fromEntries(entries) as T;
+}