title: Using "if/else" with OnClick
body: <p>First of all, is it even possible to write if/else statements directly in html with onclick attribute? And if so, why is my code not working? </p>
  
  <p>So this is a button. The "Calc.Input.value" refers to a text input and I want to display an error message if that field is 0 or blank. In all other cases I want some other things to happen as you can see. This is not relevant though, as everything after the "else" worked fine before.</p>
  
  <pre><code>&lt;INPUT TYPE="button" NAME="drop" id="dropbutton" style="background-color:#D1E8D5;" VALUE="
  Släpp ankare " OnClick="if ("Calc.Input.value == ''" || "Calc.Input.value == '0'")
  {window.alert("Please enter a number");} else 
  {document.getElementById('dropbutton').value=' Justera 
  längd ';document.getElementById('length').innerHTML =
  Calc.Input.value;document.getElementById('dropbutton').style.cssText = 'background-
  color:#FFF6B3;';}"&gt;
  </code></pre>