title: How to add to the value of a text field
body: <p>I have the form below.  Using the buttons, the value in the text field should be increase or decreased.  the decrease button works fine, but the increase button simply appends a '10' to the end of the number, so <code>100</code> will become <code>10010</code>, rather than <code>110</code>.  Can someone let me know how to fix this?</p>
  
  <pre><code>&lt;form name="hello" id="hello"&gt;
  &lt;table border=0&gt;
  &lt;tr&gt;
  &lt;td width=200&gt;
  &lt;input type=text id="input" style="height: 30px; width: 200px" name=amount value=5&gt;
  &lt;/td&gt;
  &lt;td&gt;
  &lt;table border=0&gt;
  &lt;tr height=12&gt;&lt;td width=20&gt;
  &lt;input type=button value="+" style="height: 15px; width: 25px; text-align:center; vertical-align:center; font-size:8px;" onClick="javascript:this.form.amount.value+=10;"&gt;
  &lt;/td&gt;&lt;/tr&gt;
  &lt;tr height=12&gt;&lt;td width=20&gt;
  &lt;input type=button value="-" style="height: 15px; width: 25px; text-align:center; vertical-align:center; font-size:8px;" onClick="javascript:this.form.amount.value-=10;"&gt;
  &lt;/td&gt;&lt;/tr&gt;
  &lt;/table&gt;
  &lt;/td&gt;
  &lt;/tr&gt;
  &lt;/table&gt;
  &lt;/form&gt;
  </code></pre>