• Fix unintentional use of arrow functions in some 4.1.0 builds (#138, thanks @simon04!)
• Fix usage in Web Workers (#109)
• .json() parse errors return a rejected Promise instead of throwing (#112, thanks @sunsean!)
• Improved TypeScript typings (#117 & #121, thanks @Andarist & @0x80!)
• Add support for passing URL objects to fetch() (#141, thanks @Edorka for the tip!)

Please make sure to also update to isomorphic-unfetch@3.1.0, which includes a security fix for node-fetch. (thanks @sakito21)