Please review my code

// Declare all variables at the top
let num1;
let num2;
let message;

// 2. Add an alert to announce the program with a message like "Let's do some math!"
alert("Let's do some math!");
// 3. Create a variable and use the prompt() method to collect a number from a visitor
num1 = prompt("Give me a number");
// 4. Convert that value from a string to a floating point number
num1 = parseFloat(num1);
// 5. Repeat steps 3 and 4 to create a second variable and collect a second number
num2 = prompt("Give me a second number");
num2 = parseFloat(num2);

// 6. Create a new variable -- message -- which you'll use to build
//    a complete message to print to the document
//    Start by creating a template string that includes <h1> tags as well
//    and the two input numbers. The string should look something like this:
//    `<h1>Math  with the numbers 3 and 4</h1>
//         "3 + 4 = 7"`
//         "3 * 4 = 12"
//         "3 / 4 = 0.75"
//         "3 - 4 = -1" 
//     `;

//where the two numbers are the varlues input from the user. Using Template strings to create this

// Check if input is a number
if (isNaN(num1 || num2) || (isNaN(num1 && num2))) {
  message = `Please enter a number`
} else if (num2 === 0){
  message = `<h1>Math  with the numbers ${num1} and ${num2}</h1>
             <p>${num1} + ${num2} = ${num1 + num2}</p>
             <p>${num1} * ${num2} = ${num1 * num2}</p>
             <p>Division by 0 is not possible</p>
             <p>${num1} - ${num2} = ${num1 + num2}</p>
`;
} else {
message = `<h1>Math  with the numbers ${num1} and ${num2}</h1>
            <p>${num1} + ${num2} = ${num1 + num2}</p>
            <p>${num1} * ${num2} = ${num1 * num2}</p>
            <p>${num1} / ${num2} = ${num1 / num2}</p>
            <p>${num1} - ${num2} = ${num1 - num2}</p>
`
};
// 10. Use the document.write() method to print the message variable 
//     to the web page. Open the finished.png file in this workspace
//     to see what the completed output should look like

document.write(message);