Why is "" necessary for this for loop to run? : <p>The code is below - </p>

<pre><code>for (let n = 1; n &lt;= 100; n++) {
  let output = "";
  if (n % 3 == 0) output += "Fizz";
  if (n % 5 == 0) output += "Buzz";
  console.log(output || n);
}
</code></pre>

<p>If I do not have let output = "" the code will not run.  Why is that statement required?</p>
