求助 typescript 类型声明

下面的类型声明有误

type Storable = undefined | boolean | number | string | Storable[] | { [key in string]: Storable; } 

报错: Index signature is missing in type "XXX" 有好方法能实现这种类型吗？

// 需要满足 let a: Storable a = 5 a = "string" a = [5, "string"] a = { key: { whatever: [ 5, "string", { key: 23 } ] } } // 但不能是 Function 或 Map 或其他千奇百怪的类型 // wrong a = function () { // pass } // wrong a = new Map() // wrong a = { key: new Map() }