feat(object-utilities): add getValueAssertDefined function

Author: mumenthalers

packages/utilities/src/index.ts

@@ -7,6 +7,7 @@ export * from './lib/group-by/group-by.js'
 export * from './lib/http/http-constants.js'
 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/get-value-assert-defined.function.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'

packages/utilities/src/lib/object/get-value-assert-defined.function.spec.ts

@@ -0,0 +1,50 @@
+import { getValueAssertDefined } from './get-value-assert-defined.function.js'
+
+describe('getValueAssertDefined', () => {
+  interface Test {
+    x: string | null
+    y?: boolean
+    z: number | undefined
+  }
+
+  describe('throws when not defined', () => {
+    const empty: Test = { x: null, z: undefined }
+
+    test('when null', () => {
+      expect(() => getValueAssertDefined(empty, 'x')).toThrow()
+    })
+
+    test('when undefined', () => {
+      expect(() => getValueAssertDefined(empty, 'z')).toThrow()
+    })
+
+    test('when optional', () => {
+      expect(() => getValueAssertDefined(empty, 'y')).toThrow()
+    })
+  })
+
+  describe('returns value when defined', () => {
+    const obj: Test = {
+      x: '',
+      y: false,
+      z: 0,
+    }
+
+    test('when empty string', () => {
+      expect(getValueAssertDefined(obj, 'x')).toEqual('')
+    })
+    test('when false', () => {
+      expect(getValueAssertDefined(obj, 'y')).toEqual(false)
+    })
+    test('when zero', () => {
+      expect(getValueAssertDefined(obj, 'z')).toEqual(0)
+    })
+
+    test('makes it type safe', () => {
+      const tDefined: { num: number | null } = { num: 42 }
+      // assign to variable to ensure type safety
+      const res: number = getValueAssertDefined(tDefined, 'num')
+      expect(res).toEqual(42)
+    })
+  })
+})

packages/utilities/src/lib/object/get-value-assert-defined.function.ts

@@ -0,0 +1,14 @@
+import { isDefined } from '../ts-guards/is-defined.js'
+
+/**
+ * returns the value of the provided key on given object. throws if the value is null or undefined
+ */
+export function getValueAssertDefined<T, K extends keyof T>(obj: T, key: K): NonNullable<T[K]> {
+  type X = NonNullable<T[K]>
+  const value: X | null | undefined = <any>obj[key]
+
+  if (!isDefined(value)) {
+    throw new Error(`Expected property "${String(key)}" to be defined. Was "${value}" instead`)
+  }
+  return value
+}