检查 object 是否属于类型（类型定义为数组） - TypeScript

Question

Let's say I have this

export type Hash = [ hashtype, hash ];

export type hashtype = -16 | -43 | 5 | 6;
export type hash = Buffer;

I want to write something that will check whether an object is a Hash

not implemented

isHash = (obj: any) => {
    return (obj is Hash) // pseudo code, to implement
}

So that I would have such a return:

isHash(5)                         => false    //  no hash
isHash([25, <Buffer ad 30>])      => false    //  25 is not in hashType

isHash([5, <Buffer ad 30>])       => true     //  valid

Answer 1

There isn't a general-purpose way to check whether a type matches. For your specific case, I would do something like this:

const isHash = (obj: unknown): obj is Hash => {
  if (!Array.isArray(obj)) {
    return false;
  }
  if (obj.length !== 2) {
    return false;
  }
  return [-16, -43, 5, 6].includes(obj[0]) && Buffer.isBuffer(obj[1]);
}