How can I optimize my JavaScript code to reduce execution time in the browser?

<!-- BEGIN COPY / PASTE -->
        // Example of optimizing a loop and minimizing DOM access
        const items = document.querySelectorAll('.item');
        const results = [];

        items.forEach(item => {
            // Assume some complex calculation
            const result = complexCalculation(item.textContent);
            results.push(result);
        });

        // Updating the DOM in a single operation
        const resultContainer = document.getElementById('results');
        resultContainer.innerHTML = results.join(', ');

        function complexCalculation(data) {
            // Simulate a complex calculation
            return data.length * 2;
        }
        <!-- END COPY / PASTE -->