01. Old Books

function oldBooks(input) {
    let book = input[0];
    let index = 0;
    let command;

     while(true) {
        command = input[++index];
        if (command === "No More Books" || command === book) {
            if (command === book) {
                console.log(`You checked ${--index} books and found it.`);
            } else {
                console.log(`The book you search is not here!\nYou checked ${--index} books.`);
            }
            return;
        }
    }
}

Решение с for:

function oldBooks(input) {
    let book = input[0];

    for (let i = 1; i < Number.MAX_SAFE_INTEGER; i++) {
        let command = input[i];
        if (command === "No More Books" || command === book) {
            if (command === book) {
                console.log(`You checked ${--i} books and found it.`);
            } else {
                console.log(`The book you search is not here!\nYou checked ${--i} books.`);
            }
            return;
        }
    }
}