How to check if a string is included in the type

Issue

for example(deno)

type Status = 'new' | 'update' | 'close';
itemRequest(status: Status) {...};

let userAnswer = prompt('status:');
if(/*if answer is included in Status*/){
  itemRequest(userAnswer);
}

How to check if a string is included in the type? I don't want to use an array if I can.

Solution

You cannot address a type like Status at the value level. However, you can do the following:

const statuses = ['new', 'update', 'close'] as const;
type Status = typeof statuses[number]; // enumerates the values in the array as type
...

and then in the callback:

if ((statuses as readonly string[]).includes(answer)) { // Edit: Added as readonly string[]
  userAnswser = answer;
  rl.close();
}

Another possibility would be to use an enum, which exists at both type and value level. I would prefer the array way though.

Answered By - Remirror