shallow function does not work properly for some objects

[monsonjeremy]

Bug Description

I was testing shallow because I was running into issues where sometimes I wasn't getting store updates when I expected them.

Turns out that shallow returns the wrong thing in a case like follows:

shallow({ '1': undefined }, { '2': {x: 1}})

// true

Seems like what happens is that it compares the length, which looks right. It then iterates the first object and looks for matching keys in the object. The problem is that here it resolves to undefined for both objects, but it never checks the key on the second object.

Reproduction Link

https://www.typescriptlang.org/play/?#code/PTAEDp2Tqg7A9gEwKYH0C2yCuAbFAzsAF7YEAuAhnEsIRsAG7UCWuulwBAFpewgHdwGAFYEAUMwBOoFgQCS5FFMoAjfKAC8oABQJVIgFyhqATwCUWgHygAyqYyqEucCyUryCGSzih9IgG5JShleBXc1fABROHIpFkItXWZcbBRjM0tNGx1xUFAQUAAJAEEAYQBpDMYEFiRQAGNuFAaAax8Ac1AUWPjE8lMABxQ80AAiHriEgjHZXxS08XMg6UaEDEGQlBipxO0dBZQSgBpQQ4AhLJsAb1GGhDgKUAxKQZKkw-efCmoGlAQAGagACyr1AAH4znw0u9jHAUAIQa8DtCjuBJn0CDpzMs7g8ni9BucPqjid8qHA-oCkYMIVDUihiXCETSUQzzujetNsbj8iwgTpCSVwAQWMQUKAAISabSEjmi8WWW75fJSFDkbBSXwAvgEFBBfIAX1GAK8unuj3IoAA2q0UKZTocALp+IFCpWjPkCyUAeQMLXIrixh1OcvAHXVOjtFhxoGVKtV6s12t1+s9oGNRtGao1WtAcTSQUNKxCaw2W0Uykie2SqJO9LSl2scbxltkEU8Une2k+1vsjmcrg7Xid2INazbbirneJPdJfYcThcU48I7Ho3wVvhAA9yN329OvMKd+R1-lN6AT7OD6upByT2fQAJuGwJTpJSfhUgHhKAGS-qUr3Ab94Q9BN+V0X1-QaQM5B0T9wBDS8UF3DlDljeMExzZNQB1XA9XHLME0-JIV0oTtjxQ09eRVK9SOHO9wAfGjM1AbC80lD8qK-H9QH-KUuNQ4CfyLIIAWwSlyBYB5QB4PhcEENkYUdUkwNkAU-REAMgyUo4VPZDD03Y3wCzTIj1N0AZhmpT4pRlcZ-ADWYAB9nIbI4tHsuA8FwUBXPzIZ-iBC47O0MZHJgly3JCmVtG89g1MTXMU3wsyM1GCD3zkSsVHUFBdJKSx-MlbKIjy3TLkStikzze5yzVHZMVyBN8mubouUIYxsWbTTtIxblPksQ1jnTVr2t2AguquUBepgzkJoqob0xYjKBTCHLq0aga60sfj1rK6IOuDVSquMstNgao6Cv0xsVqSnC6oulANry46GXrC5cWNcQLQIZwUHABSOh0OT+AEHQ2oAcgARkh4wJNQAEfBQephrjUBIYAJjhuNt2MaHDUNHEgA

[dbritto-dev]

@monsonjeremy you are checking ts on a js file?

[monsonjeremy]

I just wanted to make a repro example, you can disregard the types.

[dai-shi]

Interesting. Is it the same if we use the string key?

shallow({ 'a': undefined }, { 'b': {x: 1}})

// true?

[monsonjeremy]

Yeah, regardless of keys like 'a' or a it is wrong.

Looking briefly at the code, it needs to create the keys to compare by grabbing them from both objects. It can't just pull keys from the first object and check only those since the new object could have new keys (but the same length).

I'd say you could do something like

unique([...Object.keys(a), ...Object.keys(b)])

but if performance is a concern there may be a better way.

I guess you could check if the length of the above array is that same as the number of keys in Object a?

[dai-shi]

I guess you could check if the length of the above array is that same as the number of keys in Object a?

No, that's not the "shallow" comparison.

Yeah, regardless of keys like 'a' or a it is wrong.

The issue is undefined. I wonder if we could fix this without changing much of our shallow logic.

[dai-shi]

Created a failing test in #3205.

[dai-shi]

And fixed in #3205!

Thanks for reporting this!

Can you confirm if #3205 actually fixes your case using pkg.pr.new package?