The Fastly Compute JavaScript SDK's new streaming HTML rewriter in version 3.35.0 offers a high-performance solution for customizing webpage content by modifying HTML retrieved from external sources. This tool leverages an HTMLRewritingStream API that enables developers to register callbacks on CSS selectors, allowing for dynamic content manipulation such as modifying attributes or adding text to elements like h1 and div tags. By utilizing the TransformStream web standard, the rewriter processes HTML in a streaming manner, which enhances efficiency and integrates smoothly with existing pipelines for both pre- and post-processing transformations. The Fastly rewriter outperforms traditional JavaScript libraries like LinkeDOM by offering significantly faster parsing and rewriting, as demonstrated in performance benchmarks, and utilizes Cloudflare's lol-html Rust crate for real-time processing. This rewriter aims to minimize latency and optimize HTML customization while fitting seamlessly into current web standards, and is positioned as an effective tool for edge computing scenarios.