react native - Require cycles are allowed, but can result in uninitialized values. Consider refactoring to remove the need for a cycle

Question

I am receiving this warning message in my chrome console for my react-native project. Do you have any idea why I am getting this?

This is the complete message:

Require cycle: node_modules/react-native-radio-buttons/lib/index.js -> node_modules/react-native-radio-buttons/lib/segmented-controls.js -> node_modules/react-native-radio-buttons/lib/index.js

Require cycles are allowed, but can result in uninitialized values. Consider refactoring to remove the need for a cycle.

I appreciate any suggestions. Thanks

Answer 1

TL;DR: You import module A into module B and module B into module A resulting in a cycle A ?? B ?? A ?? B ?? A ..., which can result in errors. Resolve that by restructuring your modules, so that the cycle breaks.

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Detailed Answer

In javascript if you import different modules into other modules all this importing generates a dependency tree:

                                 root_module
                          ┌───────────┴───────────┐
                    sub_module_A             sub_module_B
                                         ┌────────┴────────┐
                                   sub_module_C       sub_module_D

When you run your code, all modules will be evaluated from bottom to top or from leaves to the trunk, so that for example if you import modules C and D into module B all exports of C and D are already evaluated and not undefined anymore. If module B would be evaluated before C and D, module B would be not working, because all exports from C and D would be undefined, since they have not been evaluated yet.

Still, it can be possible to form cycles in your dependency tree (this is what you got a warning for):

                                 root_module
                          ┌───────────┴───────────┐
                    sub_module_A             sub_module_B
                                                 ?? ??
                                             sub_module_C

Problem: Let's say the evaluation starts now with module C. Since it imports something from module B and it has not been evaluated yet, module C is not working correctly. All imported stuff from B is undefined. This actually is not that bad, since in the end module C is evaluated once again when everything else has been evaluated, so that also C is working. The same goes if evaluation starts with module B.

BUT: If your code relies on a working module C from the very beginning, this will result in very hard to find errors. Therefore you get this error.

How to solve: In your case the warning also gives a detailed explanation, where the cycle emerges. You import native-radio-buttons/lib/segmented-controls.js in node_modules/react-native-radio-buttons/lib/index.js and node_modules/react-native-radio-buttons/lib/index.js in native-radio-buttons/lib/segmented-controls.js. It seems like the cycle is placed inside some of your node modules. In this case there is unfortunately no way you could solve that by yourself.

If the cycle is in your own code, you have to extract some exports into a third module / file, from which you import the code into both modules previously forming the cycle.