Detailed explanation of various parameters of ajax in jquery

ajax() parameter settings is an Object object, each attribute of which is used to specify additional parameter settings required to send the request.

jQuery.ajax() can recognize the following properties of the object (they are all optional):

1.url:

Requires parameters of type String, (Defaults to the current page address) The address to send the request.

2.type:

Requires parameters of String type, and the request method (post or get) defaults to get. Note that other http request methods, such as put and delete, can also be used, but are only supported by some browsers.

3.timeout:

Requires a parameter of type Number and sets the request timeout (milliseconds). This setting will override the global setting of the $.ajaxSetup() method.

4.async:

Requires Boolean type parameters. The default setting is true. All requests are asynchronous requests. If you need to send synchronous requests, set this option to false. Note that a synchronous request will lock the browser, and the user must wait for the request to complete before other operations can be performed.

5.cache:

Requires parameters of Boolean type, the default is true (when dataType is script, the default is false), setting it to false will not load from the browser cache Requesting Information.

6.data:

Requires parameters of type Object or String, data sent to the server. If it is not a string, it will be automatically converted to string format. The get request will be appended to the url. To prevent this automatic conversion, check the processData option. The object must be in key/value format, for example {foo1:"bar1",foo2:"bar2"} is converted to &foo1=bar1&foo2=bar2. If it is an array, JQuery will automatically assign the same name to different values. For example, {foo:["bar1","bar2"]} is converted to &foo=bar1&foo=bar2.

7.dataType:

Requires parameters of String type, and expects the data type returned by the server. If not specified, JQuery will automatically return responseXML or responseText based on the http package mime information and pass it as the callback function parameter . The available types are as follows:
xml: Returns an XML document that can be processed with JQuery.
html: Returns plain text HTML information; the included script tag will be executed when inserted into the DOM.
script: Returns plain text JavaScript code. Results are not cached automatically. Unless cache parameters are set. Note that when making remote requests (not under the same domain), all post requests will be converted into get requests.
json: Return JSON data.
jsonp: JSONP format. When calling a function using the SONP form, such as myurl?callback=?, JQuery will automatically replace the last "?" with the correct function name to execute the callback function.
text: Returns a plain text string.

8.beforeSend:

requires parameters of Function type. You can modify the function of the XMLHttpRequest object before sending the request, such as adding a custom HTTP header. If false is returned in beforeSend, this ajax request can be canceled. The XMLHttpRequest object is the only parameter.​​ ​

 function(XMLHttpRequest){
  this;   //调用本次ajax请求时传递的options参数
 }

9.complete:

is required to be a parameter of Function type, a callback function that is called after the request is completed (called when the request succeeds or fails). Parameters: XMLHttpRequest object and a string describing the successful request type.​​​​

 function(XMLHttpRequest, textStatus){
    this;    //调用本次ajax请求时传递的options参数
 }

10.success: The requirement is a parameter of Function type. The callback function called after the request is successful has two parameters.

         (1) Data returned by the server and processed according to the dataType parameter.
(2) Describe the string of the state.​​​​

function(data, textStatus){
   //data可能是xmlDoc、jsonObj、html、text等等
   this;  //调用本次ajax请求时传递的options参数
}

11.error:

is required to be a parameter of Function type, which is the function to be called when the request fails. This function has 3 parameters, namely XMLHttpRequest object, error message, and captured error object (optional). The ajax event function is as follows:

function(XMLHttpRequest, textStatus, errorThrown){
    //通常情况下textStatus和errorThrown只有其中一个包含信息
    this;   //调用本次ajax请求时传递的options参数
}

12.contentType:

is required to be a String type parameter. When sending information to the server, the content encoding type defaults to "application/x-www-form- urlencoded". This default value is suitable for most applications.

13.dataFilter:

Requires parameters of Function type, a function that preprocesses the original data returned by Ajax. Provide two parameters: data and type. data is the original data returned by Ajax, and type is the dataType parameter provided when calling jQuery.ajax. The value returned by the function will be further processed by jQuery.           

function(data, type){
    //返回处理后的数据
    return data;
}

14.dataFilter:

requires parameters of Function type, a function that preprocesses the original data returned by Ajax. Provide two parameters: data and type. data is the original data returned by Ajax, and type is the dataType parameter provided when calling jQuery.ajax. The value returned by the function will be further processed by jQuery.           

function(data, type){
   //返回处理后的数据
   return data;
}

15.global：

要求为Boolean类型的参数，默认为true。表示是否触发全局ajax事件。设置为false将不会触发全局ajax事件，ajaxStart或ajaxStop可用于控制各种ajax事件。

16.ifModified：

要求为Boolean类型的参数，默认为false。仅在服务器数据改变时获取新数据。服务器数据改变判断的依据是Last-Modified头信息。默认值是false，即忽略头信息。

17.jsonp：

要求为String类型的参数，在一个jsonp请求中重写回调函数的名字。该值用来替代在"callback=?"这种GET或POST请求中URL参数里的"callback"部分，例如{jsonp:'onJsonPLoad'}会导致将"onJsonPLoad=?"传给服务器。

18.username：

要求为String类型的参数，用于响应HTTP访问认证请求的用户名。

19.password：

要求为String类型的参数，用于响应HTTP访问认证请求的密码。

20.processData：

要求为Boolean类型的参数，默认为true。默认情况下，发送的数据将被转换为对象（从技术角度来讲并非字符串）以配合默认内容类型"application/x-www-form-urlencoded"。如果要发送DOM树信息或者其他不希望转换的信息，请设置为false。

21.scriptCharset：

要求为String类型的参数，只有当请求时dataType为"jsonp"或者"script"，并且type是GET时才会用于强制修改字符集(charset)。通常在本地和远程的内容编码不同时使用。

22.jsonpCallback

为jsonp请求指定一个回调函数名。jquery会自动生成随机函数名，用这个值可以修改此名。

23. mimetype

jQuery1.5.1添加。可以用来覆盖XHR中的mimetype。

24. statusCode

jQuery1.5添加。用来定义http的返回码对应的处理函数。下面的例子定义了返回404后的处理方法。

$.ajax({   
    statusCode: {   
      404: function() {   
           alert("page not found");   
           }   
      }   
})；

25.success(data,textStatus,jqXHR)

请求成功后的回调函数。参数由服务器返回，并会根据datatype参数进行参数处理。

26.timeout

设置请求超时时间，毫秒为单位。此设置会覆盖全局设置，即所有ajax请求共享同一个超时时间。

27.traditional

设置为true，用传统的方式来序列化数据。

28.type

请求方式，get或post或put或delete。默认为get。put和delte不是得到所有的浏览器支持。

29.url

发送请求的地址。为空表示当前页。

30.username

用于响应http访问认证请求的用户名。同password配对。

31.xhr

默认在ie下是ActiveXObject而其他浏览器是XMLHttpRequest。用于重写或提供一个增强的XMLHttpRequest对象。

32.xhrFields

jQuery1.5.1添加。它可以添加到原生xhr对象上的key/value对。举个例子，你可以通过它来设置跨域的withCredentials为true。

$.ajax({   
    url: a_cross_domain_url,   
    xhrFields: {   
    withCredentials: true   
    }   
});

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