document, eventName, data)
}
// Number of active Ajax requests
$.active = 0
//settings.global为true时表示需要触发全局ajax事件
//注意这里的$.active++ === 0很巧妙，用它来判断开始，因为只有$.active等于0时$.active++ === 0才成立
function ajaxStart(settings) {
if (settings.global && $.active++ === 0) triggerGlobal(settings, null, 'ajaxStart')
}
//注意这里的 !(--$.active)同上面的异曲同工，--$.active为0，则表示$.active的值为1，这样用来判断结束，也很有意思
function ajaxStop(settings) {
if (settings.global && !(--$.active)) triggerGlobal(settings, null, 'ajaxStop')
}
// triggers an extra global event "ajaxBeforeSend" that's like "ajaxSend" but cancelable
//触发全局ajaxBeforeSend事件，如果返回false,则取消此次请求
function ajaxBeforeSend(xhr, settings) {
var context = settings.context
if (settings.beforeSend.call(context, xhr, settings) === false
关键词：zepto是啥