feat(object-utilities): add fn to pick props + assert defined from object

Author: mumenthalers

packages/utilities/src/index.ts

@@ -9,6 +9,7 @@ export * from './lib/json-stringify-replacer/json-stringify-replacer.function.js
 export * from './lib/map-values-deep/map-values-deep.js'
 export * from './lib/object/omit-props.function.js'
 export * from './lib/object/pick-props.function.js'
+export * from './lib/object/pick-props-assert-defined.function.js'
 export * from './lib/promise/make-deferred.function.js'
 export * from './lib/math/clamp.function.js'
 export * from './lib/math/random-int.js'

packages/utilities/src/lib/object/pick-props-assert-defined.function.spec.ts

@@ -0,0 +1,12 @@
+import { pickPropsAssertDefined } from './pick-props-assert-defined.function.js'
+
+describe('pickPropsAssertDefined', () => {
+  test('returns object with picked props', () => {
+    const obj = { a: true, b: 'foo', c: 42 }
+    expect(pickPropsAssertDefined(obj, ['a', 'c'])).toEqual({ a: true, c: 42 })
+  })
+  test('throws when picked prop values are null or undefined', () => {
+    const obj = { a: 'ok', b: null }
+    expect(() => pickPropsAssertDefined(obj, ['a', 'b'])).toThrow(Error)
+  })
+})

packages/utilities/src/lib/object/pick-props-assert-defined.function.ts

@@ -0,0 +1,21 @@
+import { isDefined } from '../ts-guards/is-defined.js'
+
+export type PickedPropsDefined<T, K extends keyof T> = {
+  [key in K]-?: NonNullable<T[key]>
+}
+
+/**
+ * returns an object containing the provided props with their respective value. throws if their value is null or undefined
+ */
+export function pickPropsAssertDefined<T, TProp extends keyof T>(
+  obj: T,
+  props: readonly TProp[],
+): PickedPropsDefined<T, TProp> {
+  const entries = props.map((p) => {
+    if (!isDefined(obj[p])) {
+      throw new Error(`Expected property "${String(p)}" to be defined. Was "${String(obj[p])}" instead`)
+    }
+    return [p, obj[p]]
+  })
+  return Object.fromEntries(entries)
+}