find_unused_javascript
Identify and eliminate unused JavaScript code to optimize website performance and reduce bundle size. Analyze URLs, specify device emulation, and set minimum unused byte thresholds for targeted improvements.
Instructions
Find unused JavaScript code to reduce bundle size
Input Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| device | No | Device to emulate (default: desktop) | desktop |
| minBytes | No | Minimum unused bytes to report (default: 2048) | |
| url | Yes | URL to audit |
Implementation Reference
- src/lighthouse-analysis.ts:5-44 (handler)Core handler function that runs a Lighthouse performance audit, extracts unused JavaScript from the 'unused-javascript' audit, filters items by minimum byte threshold, computes totals, and returns structured results including URL, device, total unused bytes, filtered items, and fetch time.export async function findUnusedJavaScript( url: string, device: "desktop" | "mobile" = "desktop", minBytes = DEFAULTS.MIN_UNUSED_JS_BYTES, ) { const runnerResult = await runRawLighthouseAudit(url, ["performance"], device); const { lhr } = runnerResult; const unusedJsAudit = lhr.audits["unused-javascript"]; if (!unusedJsAudit || !unusedJsAudit.details) { return { url: lhr.finalDisplayedUrl, device, totalUnusedBytes: 0, items: [], fetchTime: lhr.fetchTime, }; } // Filter items by minimum bytes const items = (unusedJsAudit.details.items || []) .filter((item: Record<string, unknown>) => (item.wastedBytes as number) >= minBytes) .map((item: Record<string, unknown>) => ({ url: item.url as string, totalBytes: item.totalBytes as number, wastedBytes: item.wastedBytes as number, wastedPercent: Math.round(((item.wastedBytes as number) / (item.totalBytes as number)) * 100), })); const totalUnusedBytes = items.reduce((sum: number, item: { wastedBytes: number }) => sum + item.wastedBytes, 0); return { url: lhr.finalDisplayedUrl, device, totalUnusedBytes, items, fetchTime: lhr.fetchTime, }; }
- src/schemas.ts:104-108 (schema)Zod schema defining input parameters for the tool: URL (validated HTTP/HTTPS), device (desktop/mobile), minBytes (minimum wasted bytes threshold, default 2048).export const unusedJavaScriptSchema = { url: baseSchemas.url, device: baseSchemas.device, minBytes: z.number().min(0).default(2048).describe("Minimum unused bytes to report (default: 2048)"), };
- src/tools/analysis.ts:20-92 (registration)MCP server tool registration for 'find_unused_javascript', providing description, input schema, and async handler that calls the core findUnusedJavaScript function, processes results into AI-friendly structured data with summaries and recommendations, handles errors, and returns formatted content.server.tool( "find_unused_javascript", "Find unused JavaScript code to reduce bundle size", unusedJavaScriptSchema, async ({ url, device, minBytes }) => { try { const result = await findUnusedJavaScript(url, device, minBytes); // Create structured, AI-friendly response const analysisData = { url: result.url, device: result.device, timestamp: result.fetchTime, thresholdBytes: minBytes, summary: { totalUnusedKB: Math.round((result.totalUnusedBytes / 1024) * 100) / 100, totalFilesAnalyzed: result.items.length, hasUnusedCode: result.items.length > 0, }, unusedFiles: result.items.map((item) => ({ filename: item.url.split("/").pop() || item.url, totalKB: Math.round((item.totalBytes / 1024) * 100) / 100, unusedKB: Math.round((item.wastedBytes / 1024) * 100) / 100, unusedPercent: item.wastedPercent, url: item.url, })), recommendations: result.items.length > 0 ? [ "Remove unused JavaScript code", "Implement code splitting", "Use tree shaking", "Add lazy loading for non-critical scripts", ] : ["No optimization needed - minimal unused code detected"], }; const summary = result.items.length > 0 ? `Found ${result.items.length} files with unused JavaScript (${analysisData.summary.totalUnusedKB}KB total)` : `No significant unused JavaScript found above ${minBytes} byte threshold`; return { content: createStructuredAnalysis("Unused JavaScript Analysis", analysisData, summary), }; } catch (error: unknown) { const errorMessage = error instanceof Error ? error.message : String(error); return { content: [ { type: "text" as const, text: `Analysis failed: ${errorMessage}`, }, { type: "text" as const, text: JSON.stringify( { error: true, url, device, message: errorMessage, timestamp: new Date().toISOString(), }, null, 2, ), }, ], isError: true, }; } }, );
- src/index.ts:27-27 (registration)Top-level call to register all analysis tools, including find_unused_javascript, on the MCP server.registerAnalysisTools(server);