TypeScript stringとnumberのUnion配列をfilterする
以下、result は string にしたいがエラーになる
const arr: (string | number)[] = [123, 456, 'AND']
const result: string = arr.find(i => typeof i === 'string')Type 'string | number' is not assignable to type 'string'.
Type 'number' is not assignable to type 'string'is を使う
https://www.typescriptlang.org/docs/handbook/advanced-types.html#user-defined-type-guards
const result: string = arr.find((i): i is string => typeof i === 'string')