title: puppeteer insert variable into page.$eval
body: <p>I want to insert a variable into an input field ...
  according to puppeeteer docs this how you do it :<a href="https://pptr.dev/#?product=Puppeteer&amp;version=v2.1.1&amp;show=api-pageevalselector-pagefunction-args-1" rel="nofollow noreferrer">Documentaion</a>
  page.$eval(selector, pageFunction[, ...args])</p>
  
  <pre><code>let VARIABLE = "01.01.2020"
  await page.$eval("input[name=date]", el =&gt; (el.value = VARIABLE));
  </code></pre>
  
  <p>Im trying to set the el.value to a variable of mine...
  Getting undefined error .. how can I pass my variable to el.value ? ??</p>