JavaScript验证表单元素是否被修改

<form>
    <input type="text" value="defaultValue 1"/>

    <input type="text" value="defaultValue 2"/>

    <textarea >defaultValue 1</textarea>

    <textarea >defaultValue 2</textarea>

    <input type="radio" name="a" />test
    <input type="radio" name="a" checked="checked"/>defaultChecked

    <input type="checkbox"  name="b"/>test
    <input type="checkbox"  name="b" checked="checked"/>defaultChecked
    <input type="checkbox"  name="b" checked="checked"/>defaultChecked


    <select>
        <option selected="selected">defaultSelected 1</option>
        <option>test</option>
        <option>test</option>
        <option>test</option>
    </select>


    <select multiple="multiple">
        <option>test</option>
        <option selected="selected">defaultSelected 1</option>
        <option selected="selected">defaultSelected 2</option>
        <option>test</option>
    </select>


    <input type="button" onclick="IsFormChanged()" value="submit"/>
</form>
<script>
function IsFormChanged() {
    var isChanged = false;
    var form = document.forms[0];
    for (var i = 0; i < form.elements.length; i++) {
        var element = form.elements[i];
        var type = element.type;
        if (type == "text" || type == "hidden" || type == "textarea" || type == "button") {
            if (element.value != element.defaultValue) {
                isChanged = true;
                break;
            }
        } else if (type == "radio" || type == "checkbox") {
            if (element.checked != element.defaultChecked) {
                isChanged = true;
                break;
            }
        } else if (type == "select-one"|| type == "select-multiple") {
            for (var j = 0; j < element.options.length; j++) {
                if (element.options[j].selected != element.options[j].defaultSelected) {
                    isChanged = true;
                    break;
                }
            }
        } else {
            //  etc...
        }
    }
    alert( isChanged?"你改变了表单的默认值.":"成功提交.");
    return isChanged;
}
</script>

 有2点注意
1，表单元素都有默认值属性，比如element.defaultValue ， element.defaultChecked  ，element.options[j].defaultSelected

2，select元素的type类型是：""select-one"或者"select-multiple"，而不是"select"。