title: Javascript String Assignment Operators
body: <p>How come I can use <code>+=</code> on a string, but I cannot use <code>-=</code> on it?</p>
  
  <p>For example...</p>
  
  <pre><code>var test = "Test";
  var arr = "&amp;#8660;"
  
  test += arr;
  alert(test);  // Shows "Test&amp;#8660;"
  
  test -= arr;
  alert(test);  // Shows "NaN"
  </code></pre>