title: What's the best way to figure out 'undefined' in several variables?
body: <p>When there are several variables and figure out even one of them is <code>undefined</code>, which code is the best one?</p>
  <p>variable is like below</p>
  <pre class="lang-js prettyprint-override"><code>const [a, b, c] = [1, '4', undefined]
  </code></pre>
  <ol>
  <li>use <code>Array.includes</code></li>
  </ol>
  <pre class="lang-js prettyprint-override"><code>[a, b, c].map(e =&gt; typeof e).includes('undefined')
  </code></pre>
  <ol start="2">
  <li>use <code>for ... of</code></li>
  </ol>
  <pre class="lang-js prettyprint-override"><code>for (const e of [a, b, c]) {
      if (typeof e === 'undefined') {
          // 'undefined' found
      }
  }
  </code></pre>
  <ol start="3">
  <li></li>
  </ol>