Several ways to submit data by POST

1. Content-Type field : The server mainly automatically obtains the encoding used by the request body according to the Content-Type attribute in the request header, and then parses the message body.
2. Four common contentTypes

1.aplication/x-www-form-urlencoded : The default attribute when the form form does not specify enctype. When submitting data, it is encoded in key = val & key1 = val1the

Note 1 : For JQuery's Ajax, the default value of Content-Type is application/x-www-form-urlencoded;charset=utf-8
as follows:

/**
     * 带file的表单提交
     */
    $("#cms-file-submit").click(function(){
        var data = $("#cms-form").serializeArray();
        var fm = new FormData()
        $(data).each(function(i){
            fm.append(this.name, this.value);
        });
        fm.append('file', $("#file")[0].files[0]);
        // console.log(fm);
        // 将获取到的数据post给服务器
        url = SCOPE.save_url;
        var jump_url = "";
        $.ajax(
            {
                url:url,
                type: 'POST',
                data: fm,
                dataType:'JSON',
                cache: false,
                contentType: false,
                processData: false,
                success:function(){
                    //1.成功的处理
                    alert(1);
                }
            }
        );
    });

So we need to set when using $.ajax()
contentType: false: (default: "application/x-www-form-urlencoded") the content encoding type when sending information to the server.
processData: false:(default: true) By default, the data option is passed The incoming data, if it is an object (technically speaking, as long as it is not a string), will be processed and converted into a query string to match the default content type application/x-www-form-urlencoded.
Reason: The data we give is the data that has been encoded with FormData, and does not require jQuery to perform string conversion.
Note 2: JQuery uses utf-8 encoding, so pay attention to this problem when doing gbk encoding.

2.multipart/form-data : When we use the form to upload files, we must make the enctyped of the form equal to this value.

3.application/json : Tell the server that the body of the message is a serialized JSON string. Can support complex structured data.

4.text/xml