How to indentify if variable is in type-CodePudding

I'm beginner in TS, so sorry for stupid question)))

I need to know if type is includes variable value

For example I have type Action = "accept" | "decline" and I need to know the result of testing by this type. Like if (Action.includes("skip")) saySkip()

Of course I know that I could create new arr with needed values but in my case I need to know if global type HTMLElementTagNameMap includes my value)

CodePudding user response：

It's possible, but only on the TypeScript side - since you're only concerned with the types, and types do not exist in emitted code, all you'll have to work with will be the resulting type. Eg

interface HTMLElementTagNameMap {
    "a": HTMLAnchorElement;
    "abbr": HTMLElement;
    "address": HTMLElement;
    // ...
}

type DoesNotExist = 'foobar';

type exists = DoesNotExist extends keyof HTMLElementTagNameMap ? true : false;

will give you an exists type of false.

But this isn't particularly useful, since it's still just a type. Whatever you're trying to do, you may need to create emitted JavaScript code instead.

// use a regular expression to transform HTMLElementTagNameMap into the below
const mapValues = [
    "a",
    "abbr",
    "address",
    // ...
];