fix(editor): Allow overriding theme from query params (#7591)

Allow overriding theme through query params.. to be able to override it
from preview iframe in webcomponent

Github issue / Community forum post (link here to close automatically):

cypress/e2e/31-demo.cy.ts

@@ -0,0 +1,23 @@
+import workflow from '../fixtures/Manual_wait_set.json';
+import { importWorkflow, vistDemoPage } from '../pages/demo';
+import { WorkflowPage } from '../pages/workflow';
+
+const workflowPage = new WorkflowPage();
+
+describe('Demo', () => {
+	it('can import template', () => {
+		vistDemoPage();
+		importWorkflow(workflow);
+		workflowPage.getters.canvasNodes().should('have.length', 3);
+	});
+
+	it('can override theme to dark', () => {
+		vistDemoPage('dark');
+		cy.get('body').should('have.attr', 'data-theme', 'dark');
+	});
+
+	it('can override theme to light', () => {
+		vistDemoPage('light');
+		cy.get('body').should('have.attr', 'data-theme', 'light');
+	});
+});

cypress/pages/demo.ts

@@ -0,0 +1,21 @@
+/**
+ * Actions
+ */
+
+export function vistDemoPage(theme?: 'dark' | 'light') {
+	const query = theme ? `?theme=${theme}` : '';
+	cy.visit('/workflows/demo' + query);
+	cy.waitForLoad();
+	cy.window().then((win) => {
+		// @ts-ignore
+		win.preventNodeViewBeforeUnload = true;
+	});
+}
+
+export function importWorkflow(workflow: object) {
+	const OPEN_WORKFLOW = {command: 'openWorkflow', workflow};
+	cy.window().then($window => {
+		const message = JSON.stringify(OPEN_WORKFLOW);
+		$window.postMessage(message, '*')
+	});
+}

cypress/pages/templates.ts

@@ -1,7 +1,5 @@
 import { BasePage } from './base';
-import { WorkflowPage } from './workflow';
 
-const workflowPage = new WorkflowPage();
 export class TemplatesPage extends BasePage {
 	url = '/templates';
 

packages/editor-ui/src/stores/ui.store.ts

@@ -37,7 +37,6 @@ import {
 	DEBUG_PAYWALL_MODAL_KEY,
 	N8N_PRICING_PAGE_URL,
 	WORKFLOW_HISTORY_VERSION_RESTORE,
-	LOCAL_STORAGE_THEME,
 } from '@/constants';
 import type {
 	CloudUpdateLinkSourceType,
@@ -64,37 +63,23 @@ import { useCloudPlanStore } from '@/stores/cloudPlan.store';
 import { useTelemetryStore } from '@/stores/telemetry.store';
 import { dismissBannerPermanently } from '@/api/ui';
 import type { BannerName } from 'n8n-workflow';
+import {
+	addThemeToBody,
+	getPreferredTheme,
+	getThemeOverride,
+	isValidTheme,
+	updateTheme,
+} from './ui.utils';
 
 let savedTheme: ThemeOption = 'system';
 try {
-	const value = localStorage.getItem(LOCAL_STORAGE_THEME) as AppliedThemeOption;
-	if (['light', 'dark'].includes(value)) {
+	const value = getThemeOverride();
+	if (isValidTheme(value)) {
 		savedTheme = value;
 		addThemeToBody(value);
 	}
 } catch (e) {}
 
-function addThemeToBody(theme: AppliedThemeOption) {
-	window.document.body.setAttribute('data-theme', theme);
-}
-
-function updateTheme(theme: ThemeOption) {
-	if (theme === 'system') {
-		window.document.body.removeAttribute('data-theme');
-		localStorage.removeItem(LOCAL_STORAGE_THEME);
-	} else {
-		addThemeToBody(theme);
-		localStorage.setItem(LOCAL_STORAGE_THEME, theme);
-	}
-}
-
-function getPreferredTheme(): AppliedThemeOption {
-	const isDarkMode =
-		!!window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)')?.matches;
-
-	return isDarkMode ? 'dark' : 'light';
-}
-
 export const useUIStore = defineStore(STORES.UI, {
 	state: (): UIState => ({
 		activeActions: [],

packages/editor-ui/src/stores/ui.utils.ts

@@ -0,0 +1,36 @@
+import type { AppliedThemeOption, ThemeOption } from '@/Interface';
+import { LOCAL_STORAGE_THEME } from '@/constants';
+
+export function addThemeToBody(theme: AppliedThemeOption) {
+	window.document.body.setAttribute('data-theme', theme);
+}
+
+export function isValidTheme(theme: string | null): theme is AppliedThemeOption {
+	return !!theme && ['light', 'dark'].includes(theme);
+}
+
+// query param allows overriding theme for demo view in preview iframe without flickering
+export function getThemeOverride() {
+	return getQueryParam('theme') || localStorage.getItem(LOCAL_STORAGE_THEME);
+}
+
+function getQueryParam(paramName: string): string | null {
+	return new URLSearchParams(window.location.search).get(paramName);
+}
+
+export function updateTheme(theme: ThemeOption) {
+	if (theme === 'system') {
+		window.document.body.removeAttribute('data-theme');
+		localStorage.removeItem(LOCAL_STORAGE_THEME);
+	} else {
+		addThemeToBody(theme);
+		localStorage.setItem(LOCAL_STORAGE_THEME, theme);
+	}
+}
+
+export function getPreferredTheme(): AppliedThemeOption {
+	const isDarkMode =
+		!!window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)')?.matches;
+
+	return isDarkMode ? 'dark' : 'light';
+}