How do i Compare three dates in Extjs?

Question

I need to compare three dates.. but i could get the result for only two dates can any one tell me how to do.. I have start date, end date and due date I have to compare like start date should be greater than end date and due date...

My code is

var required = '<span style="color:red;font-weight:bold" data-qtip="Required">*</span>';
Ext.apply(Ext.form.field.VTypes, {
    daterange : function(val, field) {
        var date = field.parseDate(val);

        if (!date) {
            return false;
        }
        if (field.startDateField && (!this.dateRangeMax || (date.getTime() != this.dateRangeMax.getTime()))) {
            var start = field.up('form').down('#' + field.startDateField);
            start.setMaxValue(date);
            start.validate();
            this.dateRangeMax = date;
        } else if (field.endDateField && (!this.dateRangeMin || (date.getTime() != this.dateRangeMin.getTime()))) {
            var end = field.up('form').down('#' + field.endDateField);
            end.setMinValue(date);
            end.validate();
            this.dateRangeMin = date;
        }
        return true;
    },

    daterangeText : 'Start date must be less than end date'
});

in the Panel i have the following code

{
    xtype : 'datefield',
    fieldLabel : 'Start Date :',
    allowBlank: false,
    afterLabelTextTpl : required,
    name : 'startDate',
    itemId : 'startdt',
    vtype : 'daterange',
    endDateField : 'enddt'
}, {
    xtype : 'datefield',
    fieldLabel : 'Due Date',
    allowBlank: false,
    afterLabelTextTpl : required,
    name : 'dueDate',
    itemId : 'duedt',
    startDateField : 'startdt',
    vtype: 'daterange'
}, {
    xtype : 'datefield',
    fieldLabel : 'Completion Date',
    afterLabelTextTpl : required,
    name : 'completionDate',
    itemId : 'enddt',
    vtype : 'daterange',
    startDateField : 'startdt'
}