设置表单的默认值、检测表单是否变更

通过动态加载表单内容，要求检测加载之后有没有变更过，可以通过defaultValue或者defaultSelected、defaultChecked属性来完成

首先，加载完成后设置默认值为当前状态的值：

//设置当前值为表单默认值
function setDefault(element) {
    if (typeof (element) == "string") {
        element = document.getElementById(element);
        if (!element) { return null; }
    }
    var type = element.type;
    if (type == "checkbox" || type == "radio") {
        element.defaultChecked = element.checked;
    }
    else if (type == "hidden" || type == "password" || type == "text" || type == "textarea") {
        element.defaultValue = element.value;
    }
    else if (type == "select-one" || type == "select-multiple") {
        for (var j = 0; j < element.options.length; j++) {
            element.options[j].defaultSelected = element.options[j].selected;
        }
    }
    var childs = element.childNodes;
    for (var i = 0; i < childs.length; i++) {
        setDefault(childs[i]);
    }
}

检测代码：

//判断表单是否改变过
function formIsDirty(form) {
    if (typeof (form) == "string") {
        form = document.getElementById(form);
        if (!form) { return null;}
    }
    for (var i = 0; i < form.elements.length; i++) {
        var element = form.elements[i];
        var type = element.type;
        if (type == "checkbox" || type == "radio") {
            if (element.checked != element.defaultChecked) {
                return true;
            }
        }
        else if (type == "hidden" || type == "password" || type == "text" || type == "textarea") {
            if (element.value != element.defaultValue) {
                return true;
            }
        }
        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) {
                    return true;
                }
            }
        }
    }
    return false;
}