feat(utilities): add extractProperty and pickProperties utilities

These utility functions make it easy to handle object values when all you want are some of their
values

src/utilities.spec.ts

@@ -0,0 +1,42 @@
+import { expect, describe, test } from 'vitest';
+import { extractProperty, pickProperties } from './utilities.js';
+
+// We may need to play fast and loose with typing here, just to test edge cases
+describe('extractProperty', () => {
+    test('works on an empty object', () => {
+        expect(extractProperty('')({} as any)).toBeUndefined()
+    })
+    test('returns undefined for a non-existent key', () => {
+        expect(extractProperty('a')({} as any)).toBeUndefined()
+    })
+    test('returns undefined for a non-existent key', () => {
+        expect(extractProperty('a')({} as any)).toBeUndefined()
+    })
+    test('returns a single value', () => {
+        expect(extractProperty('a')({ a: 42 })).toBe(42)
+    })
+})
+
+describe('pickProperties', () => {
+    test('works on an empty object', () => {
+        expect(pickProperties([''])({} as any)).toStrictEqual({})
+    })
+    test('returns undefined for a non-existent key', () => {
+        expect(pickProperties(['a'])({} as any)).toStrictEqual({})
+    })
+    test('returns undefined for a non-existent key', () => {
+        expect(pickProperties(['a'])({} as any)).toStrictEqual({})
+    })
+    test('returns an object with a single property', () => {
+        expect(pickProperties(['a'])({ a: 42 })).toStrictEqual({ a: 42 })
+    })
+    test('does not include non-existent properties', () => {
+        expect(pickProperties(['a', 'b'])({ a: 42 } as any)).toStrictEqual({ a: 42 })
+    })
+    test('does include explicitly undefined properties', () => {
+        expect(pickProperties(['a', 'b'])({ a: 42, b: undefined } as any)).toStrictEqual({ a: 42, b: undefined })
+    })
+    test('handles duplicated properties', () => {
+        expect(pickProperties(['a', 'a'])({ a: 42, b: undefined } as any)).toStrictEqual({ a: 42, })
+    })
+})

src/utilities.ts

@@ -17,6 +17,19 @@ export const drop = (t: unknown): void => void undefined
 export const asUndefined = (t: unknown) => undefined
 
 
-export const logError = (e: Error) => {
+export const logError = (e: Error) =>
     console.error(e)
-}
+
+/**
+ * Sometimes, all you're looking to do is extract a single property from and object.
+ * That's what this function does
+ */
+export const extractProperty = <O extends object>(key: keyof O) => (o: O) => o[key]
+
+/**
+ * Sometimes, you want a subset of an object, with just a few properties
+ * That's what this function does
+ */
+export const pickProperties = <O extends object>(keys: (keyof O)[]) => (o: O) => {
+    return keys.reduce((acc, key) => key in o ? ({ ...acc, [key]: o[key] }) : acc, {} satisfies Partial<O>);
+}

vitest.config.ts

@@ -2,12 +2,19 @@ import { defineConfig } from 'vitest/config'
 
 export default defineConfig({
     test: {
-    
+
         coverage: {
-            include: ['src/**'],
             enabled: true,
-            reporter: ['html', 'lcov', 'cobertura'],
+            include: ['src/**'],
+            exclude: ['coverage', 'dist'],
+            reporter: ['html', 'lcov', 'cobertura', 'json'],
+            thresholds: {
+                autoUpdate: true,
+                lines: 93,
+                statements: 93,
+                branches: 98.12,
+                functions: 85.56
+            }
         },
     },
-})
-
+})