ajax请求设置header

$.ajax({     url: "http://abc.de.com",     dataType: 'json',     type: 'GET',     beforeSend: function (xhr) {         xhr.setRequestHeader("token", "tokenvalue");     },     async: false,     cache: false,     //contentType: 'application/x-www-form-urlencoded',     success: function (sResponse) {     }  });