Comparing errors through deepEqual #3122

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1. thefourtheye

   added

   questionIssues asking questions about Node.js.Issues asking questions about Node.js.

   assertIssues and PRs related to the assert subsystem.Issues and PRs related to the assert subsystem.

   on Sep 30, 2015
2. Trott commented on Sep 30, 2015

   

   Trott

   on Sep 30, 2015

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   This looks like it's caused by code in lib/assert.js that uses Object.keys() to get all the keys in the Error objects and then compares them. The Error objects have non-enumerable keys so Object.keys(new Error('a')); returns an empty array. So the errors are determined to be equal.
3. Trott commented on Sep 30, 2015

   

   Trott

   on Sep 30, 2015

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   Possible fix: #3124
4. Trott commented on Oct 19, 2015

   

   Trott

   on Oct 19, 2015

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   I'm afraid a fix for this is unlikely to land in Node.js. The API is now locked and users are encouraged to employ userland assertion libraries instead.

   If you don't want to use a userland assertion library for whatever reason, a workaround for your case might look like this:

   assert.deepEqual(error1.message, error2.message);
   assert.deepEqual(error1.name, error2.name);
   

   Or, more thoroughly (like, if you want the stack traces to match exactly, which you typically probably don't):

   var ka = Object.getOwnPropertyNames(error1).concat(Object.getOwnPropertySymbols(error1));
   var kb = Object.getOwnPropertyNames(error1).concat(Object.getOwnPropertySymbols(error2));
   
   ka.sort();
   kb.sort();
   
   assert.deepStrictEqual(ka, kb);
   
   for (var i = ka.length - 1; i >= 0; i--) {
     console.log(ka[i]);
     assert.deepEqual(error1[ka[i]], error2[ka[i]]); // use assert.deepStrictEqual() if that's what you want
   }
   
5. Trott

   closed this as completedon Oct 19, 2015
6. Trott

   added 3 commits that reference this issue on Oct 21, 2015

   doc: add information about Assert behavior and maintenance

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   b607366

   doc: add information about Assert behavior and maintenance

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   4023c7d

   doc: add information about Assert behavior and maintenance

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