<h1>Hello World !</h1>

let numOrStr = prompt('input number or string');
console.log(numOrStr)

switch (numOrStr) {  
    case null : {
        console.log('вы отменили')
        break;
    }
    case '' : {     
        console.log('Empty String');
        break;
    }
    case  numOrStr : {   
        console.log(' number is Ba_NaN')
        break;
    }
    default: {
        console.log('OK!')
    }
}