https://www.typescriptlang.org/docs/handbook/2/narrowing.html - [[typeof型ガード]]、`typeof null`は`"object"`なので注意 - [[Truthy (JavaScript)|Truthy]] - [[Narrowing]] - [[instanceof narrowing]] - [[The in operator narrowing]] - [[Truthiness narrowing]] - [[Equality narrowing]] - [[📝TypeScriptでfilterを使ってもnarrowingによってnullやundefinedが消えない]] - [[制御フロー分析]] - [[📕TypeScriptのswitch文でcaseの考慮漏れを検知]]