Using fetch() in a scripting extension

Hello

I've creating a function to act as a rudimentary web scraper to grab some meta data like the page title, description etc using the `fetch()` api. 

In an automation, this works perfectly as expected. But in a scripting extension, my `try...catch` throws an error message of "Failed to fetch".

Are there some restrictions/limitations between automation scripts and extension scripts when it comes to using `fetch()` ?