I cannot find anything that is impure about my function

Question

Seriously, I'm getting desperate finding what the issue is. I can't find the answer for days!

React.StrictMode API causes our setState to be called twice, right? If it produces an error, then it means that somewhere in our setState callback is impure. So, which one is it?

setOrganization((initialValue) => {
    const newOrganization = { ...initialValue };

    const oldIssues = [...newOrganization.repository.issues.edges];
    const newIssues = [...data.data.organization.repository.issues.edges];

    newOrganization.repository.issues.edges = [...newIssues, ...oldIssues];

    return newOrganization;
});

On the first call, oldIssues is returning the expected value, for example, [{id: issue1}, {id: issue2}]. newIssues value is for example [{id: issue3}]
But on the second call, the oldIssues strangely turn into the combination of oldIssues and newIssues. (second call, oldIssues IS ALREADY [{id: issue1}, {id: issue2}, {id: issue3}]).
Making the second newOrganization.repository.issues.edges value has a doubled newIssues. [{id: issue1}, {id: issue2}, {id: issue3}, {id: issue3}]

Full script can be found here, on line 101: https://pastebin.com/ugsrBRTM

`newOrganization = { ...initialValue };` does a shallow copy of your object, so `initialValue` is still being modified — Nick Parsons, Jul 12 '20 at 15:26
Ohh, forget what I just asked. A silly question. I can just google it. Thank you ️ — SnekNOTSnake, Jul 12 '20 at 15:32
Holy smokes! I just changed the code to `const newOrganization = JSON.parse(JSON.stringify(initialValue));` and BAM! It works like charm! Thank you for informing me this. You have my gratitude. — SnekNOTSnake, Jul 12 '20 at 15:45

score 1 · Accepted Answer · answered Jul 12 '20 at 15:49

Thanks to Nick Parsons' comment above, I just know that object spreading only performs a shallow copy. All I need to do is to change the copy method to deep copy.

I found the method here: What is the most efficient way to deep clone an object in JavaScript?

I cannot find anything that is impure about my function

1 Answers1