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Objects with null prototype cause fast-deep-equal to throw an error

See original GitHub issue

Example code:

fastDeepEqual(Object.create(null, {a:true}), {a:true})

This will throw an error, the line below calls .valueOf() which is not a method for objects with a null prototype.

https://github.com/epoberezkin/fast-deep-equal/blob/master/src/index.jst#L51

Issue Analytics

State:
Created 4 years ago
Reactions:18
Comments:5 (2 by maintainers)

Top GitHub Comments

2reactions

epoberezkincommented, Jan 30, 2020

Thank you - I commented there.

The design decision here is to consider instances of different classes (i.e. with different prototypes in JS) as not equal, even if they have the same properties. So if null prototype support is added (which I am considering), objects in your example would not throw an exception, but would return false - I believe it is different from what you expect.

I am also considering to introduce a version of this function that ignores classes/prototypes and only checks properties, with some specific exceptions (e.g. Date and RegExp).

To address it now, any possible workaround should be used in the application code.

2reactions

thomas-jeepecommented, Jan 18, 2020

I don’t use null prototype directly, but graphql-js uses them for return values and I want to make assertions on those return values.

Some quick issue searching shows some reasoning for using null prototype.

https://github.com/graphql/graphql-js/pull/504#issuecomment-250343574

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