hasPlaceholder) {
if (!hasPlaceholder) settings.url = appendQuery(settings.url, 'callback=?')
return $.ajaxJSONP(settings)
}
var mime = settings.accepts[dataType],
baseHeaders = {},
//如果请求地址没有定请求协议，则与当前页面协议相同
protocol = /^([\w-]+:)\/\//.test(settings.url) ? RegExp.$1 : window.location.protocol,
xhr = settings.xhr(),
abortTimeout
//如果没有跨域
if (!settings.crossDomain) baseHeaders['X-Requested-With'] = 'XMLHttpRequest'
if (mime) {
baseHeaders['Accept'] = mime
if (mime.indexOf(',') > -1) mime = mime.split(',', 2)[0]
xhr.overrideMimeType && xhr.overrideMimeType(mime)
}
//如果不是GET请求，设置发送信息至服务器时内容编码类型
if (settings.contentType
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