feat: cache parsed InitialState results to Map for later use

Signed-off-by: Maksim Sukharev <antreesy.web@gmail.com>

Author: Antreesy

lib/env.d.ts

@@ -0,0 +1,8 @@
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+declare interface Window {
+    _nc_initial_state: Map<string, unknown>
+}

lib/index.ts

@@ -3,14 +3,24 @@
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
 
+if (!window._nc_initial_state) {
+	window._nc_initial_state = new Map<string, unknown>()
+}
+
 /**
  * @param app app ID, e.g. "mail"
  * @param key name of the property
  * @param fallback optional parameter to use as default value
  * @throws if the key can't be found
  */
 export function loadState<T>(app: string, key: string, fallback?: T): T {
-	const elem = <HTMLInputElement>document.querySelector(`#initial-state-${app}-${key}`)
+	const selector = `#initial-state-${app}-${key}`
+	if (window._nc_initial_state.has(selector)) {
+		return window._nc_initial_state.get(selector) as T
+	}
+
+	const elem = document.querySelector<HTMLInputElement>(selector)
+
 	if (elem === null) {
 		if (fallback !== undefined) {
 			return fallback
@@ -19,7 +29,9 @@ export function loadState<T>(app: string, key: string, fallback?: T): T {
 	}
 
 	try {
-		return JSON.parse(atob(elem.value))
+		const parsedValue = JSON.parse(atob(elem.value))
+		window._nc_initial_state.set(selector, parsedValue)
+		return parsedValue
 	} catch (e) {
 		throw new Error(`Could not parse initial state ${key} of ${app}`)
 	}

test/index.test.ts

@@ -2,9 +2,18 @@
  * SPDX-FileCopyrightText: 2023 Nextcloud GmbH and Nextcloud contributors
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
-import { expect, test } from 'vitest'
+import { expect, test, vi } from 'vitest'
 import { loadState } from '../lib'
 
+function appendInput(app: string, key: string, value: string) {
+	const input = document.createElement('input')
+	input.setAttribute('type', 'hidden')
+	input.setAttribute('id', `initial-state-${app}-${key}`)
+	input.setAttribute('value', btoa(JSON.stringify(value)))
+	// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+	document.querySelector('body')!.appendChild(input)
+}
+
 test('throw if nothing found', () => {
 	expect(() => loadState('test', 'key')).toThrow(new Error('Could not find initial state key of test'))
 })
@@ -14,14 +23,21 @@ test('return default if provided', () => {
 })
 
 test('find correct value', () => {
-	const input = document.createElement('input')
-	input.setAttribute('type', 'hidden')
-	input.setAttribute('id', 'initial-state-test-key')
-	input.setAttribute('value', btoa(JSON.stringify('foo')))
-	// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-	document.querySelector('body')!.appendChild(input)
+	appendInput('test', 'key', 'foo')
 
 	const state = loadState('test', 'key')
 
 	expect(state).toBe('foo')
 })
+
+test('returns cached value with consequent calls', () => {
+	vi.spyOn(JSON, 'parse')
+
+	appendInput('test', 'cachedKey', 'foo')
+
+	for (let i = 0; i < 10; i++) {
+		loadState('test', 'cachedKey')
+	}
+
+	expect(JSON.parse).toHaveBeenCalledTimes(1)
+})