This paper examines the architectural principles underlying modern JavaScript Edge Runtimes built on V8 Isolates as a technically and economically viable alternative to traditional cloud-centric execution models. The core isolation properties of V8 Isolates are analysed, including sub-5 ms initialization times, a baseline memory footprint of 10 KB, and per-isolate garbage collection within a shared process. A comparative performance evaluation of the Deno, Bun, and Node.js runtimes using the Hono framework is presented. The cost-efficiency boundary between Edge and conventional Serverless architectures is examined through the lens of CPU billing models. The role of the WebNN API in enabling private, on-device AI inference under GDPR and EU AI Act constraints is assessed.