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<!--info-header-start--><h1>Optional Keys </h1><blockquote><p>by yituan <a href="https://github.com/yi-tuan" target="_blank">@yi-tuan</a></p></blockquote><p><a href="https://tsch.js.org/90/play" target="_blank"></a> &nbsp;&nbsp;&nbsp;<a href="./README.zh-CN.md" target="_blank"></a> <a href="./README.ja.md" target="_blank"></a> </p><!--info-header-end-->

Implement the advanced util type OptionalKeys<T>, which picks all the optional keys into a union.

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<a href="../../README.md" target="_blank"></a> <a href="https://tsch.js.org/90/answer" target="_blank"></a> <a href="https://tsch.js.org/90/solutions" target="_blank"></a> <hr><h3>Related Challenges</h3><a href="https://github.com/type-challenges/type-challenges/blob/main/questions/00089-hard-required-keys/README.md" target="_blank"></a> <a href="https://github.com/type-challenges/type-challenges/blob/main/questions/00005-extreme-readonly-keys/README.md" target="_blank"></a> <!--info-footer-end-->