cannot catch error from fetch call when used a malformed URL

[Trenrod]

Is this a bug report?

Yes

Have you read the Contributing Guidelines?

Yes

Environment

Environment:
OS: Windows 10
Node: 6.12.3
Yarn: Not Found
npm: 3.10.10
Watchman: Not Found
Xcode: N/A
Android Studio: Version 3.0.0.0 AI-171.4443003

Packages: (wanted => installed)
react: 16.2.0 => 16.2.0
react-native: 0.53.3 => 0.53.3

Target Platform: Android 6 Emulator (From the Getting Started howto)

Steps to Reproduce

Cannot catch the fetch call when used a malformed url.

1. Call fetch() with a malformed url like 'asd' or 'https:://facebook.github.io'
2. try to catch with '.catch' when called as promise or try/catch within async/await

Expected Behavior

catch should be executed

Actual Behavior

red screen shows up with "unexpected url: [URL USED WITHIN THE CALL]"

Reproducible Demo

  async asyncFetch(url) {
    try {
      console.log('DEBUG - START FETCHING');
      const response = await fetch(url);
      console.log('DEBUG - END FETCHING');
      const xml = await response.text();
      const json = xml2json.parse(xml);
      return { data: json };
    } catch (error) {
      console.log('DEBUG - START ERROR: ' + error.message);
      throw error;
    }
  }

  const url = 'httasd:afdasdfads';
  this.asyncFetch(url)
  .catch(err => {
    console.log('DEBUG - Error: ' + err.message);
  })

Actual console output is:
DEBUG - START FETCHING

Note: Same issue like #17843

[ksegla]

fetch has been having this very bad problem for some time now, crashing apps in production whenever something it doesn't like happen. At this point, I'm looking for good alternatives :-(

[Dorentin1997]

Check if url is good and returns something. Send an request at that link with postman check what it returns.

[Trenrod]

@Dorentin1997 thank you for your comment.
Yes, a workaround can be using 'url-parse' to validate the url.
But my assumption is that if someone enters an invalid url, fetch should throw a handleble exception and not crashing the whole application.

[Dorentin1997]

Use url-parse do the logic there, if it`s wrong throw the exception there.

[Trenrod]

@Dorentin1997 again. Yes as a workaround.
Still this bug exists in the fetch implementation, which should be fixed.

[Dorentin1997]

@Trenrod Yes it`s clearly a bug, i had problems too with this. Hopefully it will be fixed.

[stale]

Hey there, it looks like there has been no activity on this issue recently. Has the issue been fixed, or does it still require the community's attention? This issue may be closed if no further activity occurs. You may also label this issue as "For Discussion" or "Good first issue" and I will leave it open. Thank you for your contributions.

[stale]

Hey there, it looks like there has been no activity on this issue recently. Has the issue been fixed, or does it still require the community's attention? This issue may be closed if no further activity occurs. You may also label this issue as "For Discussion" or "Good first issue" and I will leave it open. Thank you for your contributions.

[kelset]

This issue has been inactive for a very long time, closing. There are newer and more active issues on this subject.