First Input Delay: 2026 Guide & Best Practices

// First Input Delay Vs Interaction To Next Paint implementation with Node.js 22.x
import { performance } from 'perf_hooks';

class FirstInputDelayVsInteractionToNextPaintHandler {
  async process(data) {
    const start = performance.now();
    try {
      const result = await this.handle(data);
      console.log(`✅ Processed in ${(performance.now() - start).toFixed(2)}ms`);
      return result;
    } catch (error) {
      console.error(`❌ Error: ${error.message}`);
      throw error;
    }
  }
  
  async handle(data) {
    // Implementation
    return { success: true, ...data };
  }
}

export default FirstInputDelayVsInteractionToNextPaintHandler;

// First Input Delay Vs Interaction To Next Paint component with React 19.x
import { useCallback, useMemo } from 'react';

export default function FirstInputDelayVsInteractionToNextPaintComponent({ data }) {
  const processed = useMemo(() => {
    return data?.map(item => ({ ...item, processed: true }));
  }, [data]);
  
  const handleUpdate = useCallback(async (item) => {
    try {
      const res = await fetch('/api/update', {
        method: 'POST',
        body: JSON.stringify(item)
      });
      return await res.json();
    } catch (error) {
      console.error('Update error:', error);
      throw error;
    }
  }, []);
  
  return (
    

      
First Input Delay Vs Interaction To Next Paint
      {processed?.map(item => (
        

          {item.name}
           handleUpdate(item)}>Update
        
      ))}
    
  );
}

// First Input Delay Vs Interaction To Next Paint API route with Next.js 15.x
import type { NextRequest, NextResponse } from 'next/server';
import { NextResponse } from 'next/server';

export async function POST(request: NextRequest): Promise<NextResponse> {
  try {
    const data = await request.json();
    
    if (!data || typeof data !== 'object') {
      return NextResponse.json(
        { error: 'Invalid data' },
        { status: 400 }
      );
    }
    
    const result = await processFirstInputDelayVsInteractionToNextPaint(data);
    return NextResponse.json({ success: true, data: result });
  } catch (error) {
    return NextResponse.json(
      { error: error instanceof Error ? error.message : 'Unknown error' },
      { status: 500 }
    );
  }
}

async function processFirstInputDelayVsInteractionToNextPaint(data: any) {
  return { processed: true, ...data };
}