test(utils): add tests for updateObject util

Signed-off-by: Erik Michelson <github@erik.michelson.eu>

frontend/src/utils/update-object.ts

@@ -3,12 +3,23 @@
  *
  * SPDX-License-Identifier: AGPL-3.0-only
  */
+
+/**
+ * Takes a string-keyed object and updates it with the values of another object while ensuring that the types match.
+ * Keys in the new object, that are not present in the old object will be ignored.
+ * This is useful for updating a state object with data from an API response or local storage.
+ * The method operates in-place on the old object, instead of returning a new object to reduce memory usage.
+ *
+ * @param oldObject The object to update.
+ * @param newValues The object containing the new values.
+ */
 export const updateObject = <T extends Record<string, unknown>>(oldObject: T, newValues: T | null): void => {
   if (typeof newValues !== 'object' || newValues === null) {
     return
   }
   Object.keys(oldObject).forEach((key) => {
     if (Object.prototype.hasOwnProperty.call(newValues, key) && typeof oldObject[key] === typeof newValues[key]) {
+      // TypeScript does not allow to assign a value to a key of a generic object (as it could be potentially readonly)
       // eslint-disable-next-line @typescript-eslint/ban-ts-comment
       // @ts-expect-error
       oldObject[key] = newValues[key]

frontend/src/utils/update-objects.spec.ts

@@ -0,0 +1,45 @@
+/*
+ * SPDX-FileCopyrightText: 2024 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { updateObject } from './update-object'
+
+describe('updateObject', () => {
+  it('should not update the object if newValues is not an object', () => {
+    const oldObject = { a: 1, b: 2 }
+    // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+    // @ts-expect-error
+    updateObject(oldObject, 'abc')
+    expect(oldObject).toEqual({ a: 1, b: 2 })
+  })
+
+  it('should not update the object if newValues is null', () => {
+    const oldObject = { a: 1, b: 2 }
+    updateObject(oldObject, null)
+    expect(oldObject).toEqual({ a: 1, b: 2 })
+  })
+
+  it('should update the object with the new values', () => {
+    const oldObject = { a: 1, b: 2 }
+    const newValues = { a: 3, b: 4 }
+    updateObject(oldObject, newValues)
+    expect(oldObject).toEqual({ a: 3, b: 4 })
+  })
+
+  it('should ignore keys that are not present in the old object', () => {
+    const oldObject = { a: 1, b: 2 }
+    const newValues = { a: 3, b: 4, c: 5 }
+    updateObject(oldObject, newValues)
+    expect(oldObject).toEqual({ a: 3, b: 4 })
+  })
+
+  it('should ignore keys with different types', () => {
+    const oldObject = { a: 1, b: 2 }
+    const newValues = { a: '3', b: 4 }
+    // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+    // @ts-expect-error
+    updateObject(oldObject, newValues)
+    expect(oldObject).toEqual({ a: 1, b: 4 })
+  })
+})