Turbo mode delays async script execution on JavaScript-heavy pages

Execution Delay and Proxy Routing

Opera Turbo mode's compression proxy delays the execution of async and defer scripts by introducing an additional network hop and processing overhead. Because these scripts are fetched asynchronously, their execution is gated by the time it takes for the compression server to retrieve, compress, and deliver the asset to the client. When the free VPN is active, the request follows a dual-proxy path (Client → VPN Proxy → Turbo Compression Proxy → Origin Server), which compounds the total Round-Trip Time (RTT) and pushes back the script's DOMContentLoaded or execution trigger.

Likely Technical Explanations

While specific internal routing is proprietary, the following behaviors are typical for compression proxies of this architecture:

• Protocol Downgrading: Compression proxies often lack support for HTTP/2 multiplexing. This can force a downgrade to HTTP/1.1, eliminating the ability to fetch multiple scripts over a single connection and introducing head-of-line blocking.
• Transport Limitations: WebSockets are frequently unsupported or terminated by compression layers, forcing modern applications to fall back to less efficient long-polling mechanisms.
• Sequential Latency: The VPN adds a layer of encryption and routing, while Turbo adds a layer of transformation. These are additive, not parallel, increasing the Time to First Byte (TTFB) for every script request.

Verification Steps

To quantify the delay and identify protocol regressions, use the browser's Developer Tools (Network Tab):

1. Compare TTFB: Measure the "Time to First Byte" for a heavy .js file with Turbo disabled vs. enabled.
2. Check Protocol: Enable the "Protocol" column in the Network panel to verify if h2 (HTTP/2) is replaced by http/1.1.
3. Test WebSockets: Attempt to connect to a WebSocket echo server; if the handshake fails only when Turbo is active, the proxy is stripping the Upgrade header.

Missing Diagnostic: Are you observing this behavior on the mobile or desktop version of the browser? The compression logic and proxy routing differ significantly between platforms.