JSFiddle - React, Tailwind, and code Playground

JavaScript

function isVowel(char){

    if(typeof char == 'string' && char.length > 1){
        console.log('not a char');
        return 'not a char';
    } else {
        if (
            char.toLowerCase() === 'a'
            || char.toLowerCase() === 'e'
            || char.toLowerCase() === 'i'
            || char.toLowerCase() === 'o'
            || char.toLowerCase() === 'u'
        ){
            console.log(char, true);
            return true;
        } else {
            console.log(char, false);
            return false;
        }
    }
}

document.writeln(isVowel('a'));
document.writeln(isVowel('e'));
document.writeln(isVowel('l'));