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

See original GitHub issue

Browser: Chrome/49.0.2623.112
Os: Windows NT 6.0
Error: Cannot redefine property: hasInstance

Error as described in Datadog

TypeError: Cannot redefine property: hasInstance
  at Function.defineProperty @ <anonymous>
  at <anonymous> @ https://polyfill.io/v3/polyfill.min.js?features=default%2Ces2015%2CNodeList.prototype.forEach%2Cfetch:3:17056
  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 (Windows NT 6.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.112 Safari/537.36

I tried creating a simple html and spoofing the user agent, but it still happened.

test.html

<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>test</title>
    <script crossorigin="anonymous" src="https://polyfill.io/v3/polyfill.min.js?features=Symbol.hasInstance"></script>
  </head>
  <body>
    test
  </body>
</html>

Error as described in Chrome Console

Uncaught TypeError: Cannot redefine property: hasInstance
    at Function.defineProperty (<anonymous>)
    at polyfill.min.js?features=Symbol.hasInstance:3
    at polyfill.min.js?features=Symbol.hasInstance:3

I think it’s the correct behavior to be called in Chrome version 49. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/hasInstance

I think the chrome = "< 50" setting in the config for hasInstance is also correct. https://github.com/Financial-Times/polyfill-library/blob/master/polyfills/Symbol/hasInstance/config.toml#L13

I check into it so far, but I’m just not sure.

Please confirm the above.

Issue Analytics

State:
Created 3 years ago
Comments:5

Top GitHub Comments

2reactions

JakeChampioncommented, Dec 16, 2020

Uh, no. I’ve been spoofed by a user agent, but the version of Chrome itself is newer so it’s an incorrect action?

Correct, spoofed user agents is not something polyfill.io supports. You need to use the real Chrome 49 to test it, which I’ve done above and shown is working correctly

1reaction

JakeChampioncommented, Dec 16, 2020

I’ve tested this in Chrome 49 and it does not throw an error:

This is the site I tested with: – https://jsbin.com/judugiqari/edit?html,output

<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>test</title>
  </head>
  <body>
  </body>
  <script crossorigin="anonymous" src="https://polyfill.io/v3/polyfill.min.js?features=Symbol.hasInstance"></script>
  <script>
    document.body.innerHTML = 'Symbol.hasInstance: ' + !!Symbol.hasInstance
    </script>
</html>