Do not use constructor.name to check object

isAbortSignal and isBlob use constructor.name only to check.

https://github.com/bitinn/node-fetch/blob/bf8b4e8db350ec76dbb9236620f774fcc21b8c12/src/request.js#L36-L43

https://github.com/bitinn/node-fetch/blob/95286f52bb866283bc69521a04efe1de37b26a33/src/body.js#L364-L378

However, constructor.name can be rewrited. So, for example, webpack4 with production mode will break constructor.name of AbortSignal that will be rewritten to "s".

So, Expected signal to be an instanceof AbortSignal Error was occured (ref: https://github.com/yumetodo/vscode-google-photos-uploader/issues/11 )

isURLSearchParams is adopting good implementation (ref: https://github.com/bitinn/node-fetch/issues/296#issuecomment-307598143, https://github.com/bitinn/node-fetch/pull/297/commits/302992d68e75748a7781c52e868b4fde7925325f ). Object.prototype.toString() will call Symbol.toStringTag propaty which is not writable(see MDN)

https://github.com/bitinn/node-fetch/blob/95286f52bb866283bc69521a04efe1de37b26a33/src/body.js#L346-L362

Of course, I know that there are two workarounds for webpack4:

1. Set optimization.minimize to false (ref: https://github.com/webpack/webpack/issues/6841#issuecomment-376129163)
2. Specify minimizer manually and set keep_fnames to true (ref: https://github.com/CartoDB/carto-vl/pull/1066)

However, rely on constructor.name is a bad idea, I think.

[Richienb]

Fixed in #673

[bitinn]

OK, we will drop constructor.name in favor of toStringTag in v3 release where applicable.