title: Uncaught ReferenceError: url is not defined
body: <p>So I created a an iphone out of pure css and I am trying to make the screen change on click to make it interactive. I am new to java script, just started learning about it a week or so ago, and browser is telling me "Uncaught ReferenceError: url is not defined" not sure what i'm doing wrong. Any advice on why it is telling me this, so I make sure not to make the same mistake in the future. I am sure it is a simple fix just not sure how to go about it.</p>
  
  <pre><code>&lt;div id="iphone-border"&gt;
              &lt;div id="off-button"&gt;&lt;/div&gt;
              &lt;div id="mute-button"&gt;&lt;/div&gt;
              &lt;div id="volume-up-button"&gt;&lt;/div&gt;
              &lt;div id="volume-down-button"&gt;&lt;/div&gt;
              &lt;div id="side-lines-1"&gt;&lt;/div&gt;
              &lt;div id="side-lines-2"&gt;&lt;/div&gt;
              &lt;div id="iphone-color"&gt;
                  &lt;div id="camara"&gt;&lt;/div&gt;
                  &lt;div id="sensor"&gt;&lt;/div&gt;
                  &lt;div id="speaker"&gt;&lt;/div&gt;
                  &lt;div id="iphone-screen" onClick="this.style.backgroundImage=url(img/phone-screen.jpg);" &gt;
  
                  &lt;/div&gt;
                  &lt;div id="home-button-border"&gt;
                      &lt;div id="home-button-color"&gt;&lt;/div&gt;
                  &lt;/div&gt;
  
              &lt;/div&gt;
          &lt;/div&gt;
  </code></pre>