使用装饰者模式实现ajax loading效果

var myajax = $.ajax;
$.ajax = function (params) {
    alert('load')
    myajax.call(this, params)
}

$.ajax({
    url: 'http://xuexi.hzcqt.com/api/v1/jpkc/course/category_tree.xhtml',
    type: "GET", async: true, xhrFields: { withCredentials: true },
    traditional: true,//可以上传数组
    success: function (data) {
        alert(data)
    },
    error: function (err) {
        alert('err')
    }
});