How to Create a Simple Online Calculator

HTML Code

<br/><br/><br/><br/>

<label id="calculation"></label>
<br/>
            
            
<table style="text-align: left; width: 265px; height: 118px;" border="0"
            cellpadding="2" cellspacing="2">
<tr>
<td colspan="4" rowspan="1" style="vertical-align: top;"> <div id='mainarea' contenteditable style="width:100%; height:20px; border: 1px solid black;"></div>
</td>
</tr>
<tr>
<td style="vertical-align: top; text-align: center;" >
<input TYPE="button" NAME="7"   VALUE="  7  " onclick="updateTextbox(7)">
<input TYPE="button" NAME="8"   VALUE="  8  " onclick="updateTextbox(8)">
<input TYPE="button" NAME="9"   VALUE="  9  " onclick="updateTextbox(9)">
<input TYPE="button" NAME="+"  VALUE="  +  " onclick="updateTextbox('+')">
<br>
<input TYPE="button" NAME="4"   VALUE="  4  " onclick="updateTextbox(4)">
<input TYPE="button" NAME="5"   VALUE="  5  " onclick="updateTextbox(5)">
<input TYPE="button" NAME="6"   VALUE="  6  " onclick="updateTextbox(6)">
<input TYPE="button" NAME="-" VALUE="  -  " onclick="updateTextbox('-')">
<br>
<input TYPE="button" NAME="1"   VALUE="  1  " onclick="updateTextbox(1)">
<input TYPE="button" NAME="2"   VALUE="  2  " onclick="updateTextbox(2)">
<input TYPE="button" NAME="3"   VALUE="  3  " onclick="updateTextbox(3)">
<input TYPE="button" NAME="*" VALUE="  x  " onclick="updateTextbox('*')">
<br>
<input TYPE="button" NAME="c" VALUE="  c  " onclick="reset();">
<input TYPE="button" NAME="0"  VALUE="  0  " onclick="updateTextbox(0)">
<input TYPE="button" NAME="="  VALUE="  =  " onclick="result();">
<input TYPE="button" NAME="/"   VALUE="  /  " onclick="updateTextbox('/')">
</td>
</tr>
</table>

Javascript Code