Stream reading a Response object may not be available while a progress callback is specified

[Xmader]

The body property may not be available on a Response object to do streaming, e.g., when using a fetch polyfill.

[xenova]

Thanks for the PR! Very interesting. 👀 Do you have a link to some documentation which states that the response body may be undefined in that (or some other) polyfill?

[Xmader]

Hi @xenova, Thanks for the reply!
I couldn't find anywhere in the documentation of that polyfill, but I found a few issues (JakeChampion/fetch#1454, JakeChampion/fetch#746, JakeChampion/fetch#198 (comment)) saying Response.body is undefined and would unlikely be supported ever.

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Another polyfill https://github.com/developit/unfetch says it only supports a subset of the Response class, response.body is not included.

[xenova]

Thanks for the info 👍 And just for interest's sake, what environment are you running in that requires a fetch polyfill?

[lindboe]

And just for interest's sake, what environment are you running in that requires a fetch polyfill?

@xenova Most React Native apps use a fetch polyfill. (Some use expo/fetch which is a native module implementation.)

I am not using this library, just came across this while researching some changes to the fetch polyfill, so I figured I would answer.

[xenova]

As of Transformers.js v4, we expose a custom env.fetch option, which you can use if you need to support this.