Handles a "fetch-text" message: downloads a text file (e.g. GPX) and returns it. Perf 6.3.1: off-load the GPX network call to the Worker — DOMParser parsing stays on the main thread.
Received message data
Handles a "fetch-text" message: downloads a text file (e.g. GPX) and returns it. Perf 6.3.1: off-load the GPX network call to the Worker — DOMParser parsing stays on the main thread.