How do you test application performance and prevent regressions?

// benchmark.test.js
describe('Performance benchmarks', () => {
  test('array sort performance', () => {
    const largeArray = Array.from({ length: 10000 }, () => Math.random());
    
    const start = performance.now();
    largeArray.sort((a, b) => a - b);
    const duration = performance.now() - start;
    
    expect(duration).toBeLessThan(50); // Should complete in 50ms
  });

  test('component render time', async () => {
    const start = performance.now();
    
    const { container } = render(<LargeList items={Array(1000).fill({})} />);
    
    const duration = performance.now() - start;
    expect(duration).toBeLessThan(100);
  });
});

// Using benchmark.js for detailed profiling
import Benchmark from 'benchmark';

const suite = new Benchmark.Suite();

suite
  .add('RegExp#test', () => {
    /o/.test('Hello World!');
  })
  .add('String#includes', () => {
    'Hello World!'.includes('o');
  })
  .on('complete', function() {
    console.log('Fastest is ' + this.filter('fastest').map('name'));
  })
  .run();