jquery中ajax处理跨域的三大方式_jquery

  header("Access-Control-Allow-Origin:*");
  /*星号表示所有的域都可以接受，*/
 header("Access-Control-Allow-Methods:GET,POST");

 /*当前网址是localhost:3000*/
 js代码
 
 $.ajax({
   type:"get",
   url:"http://localhost:3000/showAll",/*url写异域的请求地址*/
   dataType:"jsonp",/*加上datatype*/
   jsonpCallback:"cb",/*设置一个回调函数，名字随便取，和下面的函数里的名字相同就行*/
   success:function(){
    。。。
   }
  });

 /*而在异域服务器上，*/
 app.js
 app.get('/showAll',students.showAll);/*这和不跨域的写法相同*/
 
  
 /*在异域服务器的showAll函数里，*/

 var db = require("./database");

 exports.showAll = function(req,res){

 /**设置响应头允许ajax跨域访问**/
 res.setHeader("Access-Control-Allow-Origin","*");
  /*星号表示所有的异域请求都可以接受，*/
 res.setHeader("Access-Control-Allow-Methods","GET,POST");

 var con = db.getCon();
 con.query("select * from t_students",function(error,rows){
  if(error){
   console.log("数据库出错："+error);
  }else{
   /*注意这里，返回的就是jsonP的回调函数名+数据了*/
   res.send("cb("+JSON.stringify(r)+")");
  }
 });
 }

//跨域（可跨所有域名）
$.getJSON("http://user.hnce.com.cn/getregion.aspx?id=0&jsoncallback=?",function(json){ 
//要求远程请求页面的数据格式为： ?(json_data) //例如： //?([{"_name":"湖南省","_regionId":134},{"_name":"北京市","_regionId":143}]) alert(json[0]._name); 
}); 

$.getJSON("http://user.hnce.com.cn/getregion.aspx?id=0&jsoncallback=?",function(json){ 
//要求远程请求页面的数据格式为： ?(json_data) //例如： //?([{"_name":"湖南省","_regionId":134},{"_name":"北京市","_regionId":143}]) alert(json[0]._name); 
}); 

<script src="http://common.cnblogs.com/script/jquery.js" type="text/javascript"></script> 
<script type="text/javascript"> 
//跨域（可跨所有域名） 
$.getJSON("http://e.hnce.com.cn/tools/ajax.aspx?jsoncallback=?", { id: 0, action: 'jobcategoryjson' }, function(json) { alert(json[0].pid); alert(json[0].items[0]._name); });　 
 </script> 

<script src="http://common.cnblogs.com/script/jquery.js" type="text/javascript"></script> 
<script type="text/javascript"> 
//跨域（可跨所有域名） 
$.getJSON("http://e.hnce.com.cn/tools/ajax.aspx?jsoncallback=?", { id: 0, action: 'jobcategoryjson' }, function(json) { alert(json[0].pid); alert(json[0].items[0]._name); });　 
 </script> 

<script type="text/javascript" src="http://domain2.com/getjson?jsonp=parseResponse"> </script> 
响应值：parseResponse({"Name": "Cheeso", "Rank": 7}) 
<script type="text/javascript" src="http://domain2.com/getjson?jsonp=parseResponse"> </script> 
响应值：parseResponse({"Name": "Cheeso", "Rank": 7}) 

getJSON: function( url, data, callback ) {
   return jQuery.get(url, data, callback, "json");
  },
 

   get: function( url, data, callback, type ) {
    // shift arguments if data argument was omited
    if ( jQuery.isFunction( data ) ) {
     type = type || callback;
     callback = data;
     data = null;
    }
  
    return jQuery.ajax({
     type: "GET",
     url: url,
     data: data,
     success: callback,
     dataType: type
    });

 // Build temporary JSONP function
  if ( s.dataType === "json" && (s.data && jsre.test(s.data) || jsre.test(s.url)) ) {
   jsonp = s.jsonpCallback || ("jsonp" + jsc++);
 
   // Replace the =? sequence both in the query string and the data
   if ( s.data ) {
    s.data = (s.data + "").replace(jsre, "=" + jsonp + "$1");
   }
 
   s.url = s.url.replace(jsre, "=" + jsonp + "$1");
 
   // We need to make sure
   // that a JSONP style response is executed properly
   s.dataType = "script";
 
   // Handle JSONP-style loading
   window[ jsonp ] = window[ jsonp ] || function( tmp ) {
    data = tmp;
    success();
    complete();
    // Garbage collect
    window[ jsonp ] = undefined;
 
    try {
     delete window[ jsonp ];
    } catch(e) {}
 
    if ( head ) {
     head.removeChild( script );
    }
   };
  }
 
  if ( s.dataType === "script" && s.cache === null ) {
   s.cache = false;
  }
 
  if ( s.cache === false && type === "GET" ) {
   var ts = now();
 
   // try replacing _= if it is there
   var ret = s.url.replace(rts, "$1_=" + ts + "$2");
 
   // if nothing was replaced, add timestamp to the end
   s.url = ret + ((ret === s.url) ? (rquery.test(s.url) ? "&" : "?") + "_=" + ts : "");
  }

  // If data is available, append data to url for get requests
  if ( s.data && type === "GET" ) {
   s.url += (rquery.test(s.url) ? "&" : "?") + s.data;
  }
 
  // Watch for a new set of requests
  if ( s.global && ! jQuery.active++ ) {
   jQuery.event.trigger( "ajaxStart" );
  }
 
  // Matches an absolute URL, and saves the domain
  var parts = rurl.exec( s.url ),
   remote = parts && (parts[1] && parts[1] !== location.protocol || parts[2] !== location.host);
 
 // If we're requesting a remote document
  // and trying to load JSON or Script with a GET
  if ( s.dataType === "script" && type === "GET" && remote ) {
   var head = document.getElementsByTagName("head")[0] || document.documentElement;
   var script = document.createElement("script");
   script.src = s.url;
   if ( s.scriptCharset ) {
    script.charset = s.scriptCharset;
   }
 
   // Handle Script loading
   if ( !jsonp ) {
    var done = false;
 
    // Attach handlers for all browsers
    script.onload = script.onreadystatechange = function() {
     if ( !done && (!this.readyState ||
       this.readyState === "loaded" || this.readyState === "complete") ) {
      done = true;
      success();
      complete();
 
      // Handle memory leak in IE
      script.onload = script.onreadystatechange = null;
      if ( head && script.parentNode ) {
       head.removeChild( script );
      }
     }
    };
   }
 
   // Use insertBefore instead of appendChild to circumvent an IE6 bug.
   // This arises when a base node is used (#2709 and #4378).
   head.insertBefore( script, head.firstChild );
 
   // We handle everything using the script element injection
   return undefined;
  }