SnakeCase

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题目

Create a SnakeCase<T> generic that turns a string formatted in camelCase into a string formatted in snake_case.

A few examples:

type res1 = SnakeCase<"hello">; // => "hello"
type res2 = SnakeCase<"userName">; // => "user_name"
type res3 = SnakeCase<"getElementById">; // => "get_element_by_id"

解答

type SnakeCase<T> = T extends `${infer A}${infer R}`
  ? Uppercase<A> extends A
    ? `_${Lowercase<A>}${SnakeCase<R>}`
    : `${A}${SnakeCase<R>}`
  : "";