[Bug] Chrome/49 - Cannot redefine property: isConcatSpreadable

• Browser: Chrome/49.0.2623.112
• Os: Mac OS X 10.6.8
• Error: Cannot redefine property: isConcatSpreadable

Error as described in Datadog

TypeError: Cannot redefine property: isConcatSpreadable
  at Function.defineProperty(native) @ undefined
  at <anonymous> @ https://polyfill.io/v3/polyfill.min.js?features=default%2Ces2015%2CNodeList.prototype.forEach%2Cfetch:3:17130
  at <anonymous> @ https://polyfill.io/v3/polyfill.min.js?features=default%2Ces2015%2CNodeList.prototype.forEach%2Cfetch:3:25647

User-Agent as described in Datadog

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.112 Safari/537.36

Our polyfill.io url

https://polyfill.io/v3/polyfill.min.js?features=default%2Ces2015%2CNodeList.prototype.forEach%2Cfetch

I tried spoofing the user agent and using only isConcatSpreadable, so polyfill was called for.

URL: https://polyfill.io/v3/polyfill.min.js?features=Symbol.isConcatSpreadable
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.112 Safari/537.36

I think the correct behavior is that it will not be called if the chrome version is 48 or higher. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/isConcatSpreadable

The config for isConcatSpreadable is chrome = "<48". https://github.com/Financial-Times/polyfill-library/blob/master/polyfills/Symbol/isConcatSpreadable/config.toml#L13

Please confirm the above.

[JakeChampion]

I’ll be doing a release today 👍

[JakeChampion]

Symbol.isConcatSpreadable was changed to serve to Chrome lower than 48 yesterday in polyfill-library.

polyfill.io is not using the latest version of polyfill-library yet, the version it is using does serve Symbol.isConcatSpreadable to Chrome versions lower than 50, which is what you are seeing.