JacobWeisenburger

/**
CORS blocks this request from the browser, so you will need to run this code on the server.
*/
async function checkIfYouTubeChannelIsLive ( channelId: string ) {
    const liveCheckURL = `https://www.youtube.com/embed/live_stream?channel=${ channelId }`
    const responseText = await fetch( liveCheckURL ).then( res => res.text() )
    const isLive = responseText.indexOf( 'This video is unavailable' ) < 0
    return isLive
}

JacobWeisenburger

type ValidateType<T extends string> =
    T extends 'bad' ? 'Error message'
    : T extends 'another bad' ? 'Another error message'
    : T extends 'Error message' | 'Another error message' ? `Can't use '${ T }'`
    : T

function fn<T extends string> ( arg: ValidateType<T> ) { }

fn( 'this should work' ) // works
fn( 'bad' ) // Argument of type '"bad"' is not assignable to parameter of type '"Error message"'.