Autofill UI + React SPAs

### Summary

Eventually add some content around React Single Page Apps and dealing with modal vs conditional UI

@MasterKale created this: https://gist.github.com/MasterKale/30c739d460a8d1d5e7bbbe66b8847f56

### Details

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### Proposed Content Type

Best Practice

### Proposed Content Title

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### Related Articles

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