title: Checkbox returns true even when unchecked
body: <p>I am having trouble with an if-statement. In this statement i want to check if a checkbox is checked true (or isSelected) then it shall proceed with the instruction to disable a textarea. This part is working fine. But unfortunately if the checkbox is unchecked it still disabling the textarea, but it shouldn't. It should leave the textarea enabled.</p>
  
  <pre><code>function auswahl_bestaetigen(){
  
      tweet = document.getElementById("chk_tweet")
      twitter = document.getElementById("twitter")
  
      if (tweet.isSelected = true)
                  twitter.disabled = true
      else if (tweet.isSelected = false) 
                  twitter.disabled = false    
  }
  </code></pre>
  
  <p>i hope someone can help me with this problem. Thanks in advance :)</p>