feat: add JavaScript learning section with starter lessons and sidebar section headers

Implementation following plan:
- S01: Foundation: schema, section config, and router
- S02: Install CodeMirror JavaScript language support
- S03: Create JavaScript lesson JSON files (variables, DOM, events)
- S04: Register JavaScript lessons in module stores
- S05: Add JavaScript validation logic
- S06: Add JavaScript mode to LessonEngine preview rendering
- S07: Add JavaScript mode to CodeEditor
- S08: Update app.js for JavaScript mode support
- S09: Update navigation HTML and CSS theming for JavaScript section
- S10: Add section grouping headers in sidebar navigation
- S11: Update and write tests

src/helpers/renderer.js

@@ -2,6 +2,7 @@
  * Renderer - Handles UI updates for the CSS learning platform
  */
 import { t } from "../i18n.js";
+import { getModuleSection, getSection, getSectionList } from "../config/sections.js";
 
 /**
  * Compute lesson difficulty based on lesson structure
@@ -72,8 +73,24 @@ export function renderModuleList(container, modules, onSelectModule, onSelectLes
 		}
 	}
 
+	// Group modules by section for headers
+	let currentSectionId = null;
+
 	// Create list items for each module
 	modules.forEach((module) => {
+		// Insert section header when section changes
+		const sectionId = getModuleSection(module);
+		if (sectionId !== currentSectionId && !module.excludeFromProgress) {
+			currentSectionId = sectionId;
+			const section = getSection(sectionId);
+			if (section) {
+				const header = document.createElement("h3");
+				header.className = "sidebar-section-header";
+				header.textContent = section.title;
+				header.style.borderLeftColor = section.color;
+				container.appendChild(header);
+			}
+		}
 		// Create module container
 		// Use native <details>/<summary> for expand/collapse
 		const moduleContainer = document.createElement("details");

src/helpers/router.js

@@ -27,7 +27,7 @@ export const RouteType = {
 /**
  * Valid section IDs
  */
-const SECTIONS = ["css", "html", "markdown"]; // tailwind temporarily disabled
+const SECTIONS = ["css", "html", "markdown", "javascript"]; // tailwind temporarily disabled
 
 /**
  * Valid language codes for URL-based switching

src/helpers/validator.js

@@ -10,6 +10,8 @@ export function validateUserCode(userCode, lesson) {
 			return validateHtmlCode(userCode, lesson);
 		case "tailwind":
 			return validateTailwindClasses(userCode, lesson);
+		case "javascript":
+			return validateJavaScriptCode(userCode, lesson);
 		case "css":
 		default:
 			return validateCssCode(userCode, lesson);
@@ -204,6 +206,80 @@ function validateHtmlCode(userHtml, lesson) {
 	return result;
 }
 
+/**
+ * Validate user JavaScript code against the lesson requirements
+ * @param {string} userCode - User submitted JavaScript code
+ * @param {Object} lesson - The current lesson object
+ * @returns {Object} Validation result with isValid and message properties
+ */
+function validateJavaScriptCode(userCode, lesson) {
+	if (!lesson || !lesson.validations) {
+		return { isValid: true, message: "No validations specified for this lesson." };
+	}
+
+	const validations = lesson.validations;
+
+	let result = {
+		isValid: true,
+		validCases: 0,
+		totalCases: validations.length,
+		message: "Your CODE looks CRISPY!"
+	};
+
+	for (const validation of validations) {
+		const { type, value, message, options } = validation;
+		let validationPassed = false;
+
+		switch (type) {
+			case "contains":
+				validationPassed = containsValidation(userCode, value, options);
+				if (!validationPassed) {
+					result = {
+						...result,
+						isValid: false,
+						message: message || `Your code should include "${value}".`
+					};
+				}
+				break;
+
+			case "not_contains":
+				validationPassed = !containsValidation(userCode, value, options);
+				if (!validationPassed) {
+					result = {
+						...result,
+						isValid: false,
+						message: message || `Your code should not include "${value}".`
+					};
+				}
+				break;
+
+			case "regex":
+				validationPassed = regexValidation(userCode, value, options);
+				if (!validationPassed) {
+					result = {
+						...result,
+						isValid: false,
+						message: message || "Your code does not match the expected pattern."
+					};
+				}
+				break;
+
+			default:
+				console.warn(`Unknown JavaScript validation type: ${type}`);
+				validationPassed = true;
+		}
+
+		if (validationPassed) {
+			result.validCases++;
+		} else {
+			return result;
+		}
+	}
+
+	result.validCases = validations.length;
+	return result;
+}
+
 function validateTailwindClasses(userClasses, lesson) {
 	if (!lesson || !lesson.validations) {
 		return { isValid: true, message: "No validations specified for this lesson." };