javascript 注册事件

var inputs = 0;
function addContact(){
    var table = document.getElementById('contacts');

    var tr = document.createElement('TR');
    var td1 = document.createElement('TD');
    var td2 = document.createElement('TD');
    var td3 = document.createElement('TD');
    var inp1 = document.createElement('INPUT');
    var inp2 = document.createElement('INPUT');

    if(inputs>0){
        var img = document.createElement('IMG');
        img.setAttribute('src', 'delete.gif');
        img.onclick = function(){/////////////
            removeContact(tr);
        }
        td1.appendChild(img);
    }

    inp1.setAttribute("Name", "Name" +inputs);
    inp2.setAttribute("Name", "Email"+inputs);

    table.appendChild(tr);
    tr.appendChild(td1);
    tr.appendChild(td2);
    tr.appendChild(td3);
    td2.appendChild(inp1);
    td3.appendChild(inp2);

    inputs++;
}
function removeContact(tr){
    tr.parentNode.removeChild(tr);
}

<table>
   <tbody id="contacts">
    <tr>
    <td colspan="3"><a href="javascript:addContact();">Add a Contact</a></td>
    </tr>
    <tr>
    <td></td>
    <td>Name</td>
    <td>Email</td>
    </tr>
   </tbody>
</table>