注意:这个答案并没有直接回答问题，而是给出了说明和替代方案。

人们通常使用FormData来允许他们上传文件，有三种方法可以做到这一点，我会在这个回答中详细提到它们。

1. 直接从表单中获取数据

为此，您需要在每个输入中拥有名称和值属性，然后告诉FormData从表单DOM中获取值;

let formData = new FormData(data.target as HTMLFormElement)

优点:

你不需要使用JS解决方案来获取这些值。 原生支持嵌套数据，数组等…

缺点:

您需要确保所有需要的数据都作为值属性添加到输入dom上

2. 用JS转换数据 如果你把值存储在变量中，那么你可以使用JS将它们附加到FormData中。

优点:

是否可以根据需要进行操作 你不需要在输入dom中有值属性

缺点:

自定义复杂JS附加嵌套数据到FormData对象 您需要将值存储在一个变量中

3.在单独的请求中上传文件

您可以为文件上传输入创建一个单独的表单。

优点:

您不需要等待上传提交 您不需要担心将所有数据追加到FormData对象，您只追加文件。

缺点:

在创建实体本身之前，您需要在后端处理这些上传 您需要在前端和后端处理删除文件

我有一个场景，在构造表单数据时，嵌套的JSON必须以线性方式序列化，因为这是服务器期望值的方式。所以，我写了一个小的递归函数来翻译JSON，就像这样:

{
   "orderPrice":"11",
   "cardNumber":"************1234",
   "id":"8796191359018",
   "accountHolderName":"Raj Pawan",
   "expiryMonth":"02",
   "expiryYear":"2019",
   "issueNumber":null,
   "billingAddress":{
      "city":"Wonderland",
      "code":"8796682911767",
      "firstname":"Raj Pawan",
      "lastname":"Gumdal",
      "line1":"Addr Line 1",
      "line2":null,
      "state":"US-AS",
      "region":{
         "isocode":"US-AS"
      },
      "zip":"76767-6776"
   }
}

变成这样:

{
   "orderPrice":"11",
   "cardNumber":"************1234",
   "id":"8796191359018",
   "accountHolderName":"Raj Pawan",
   "expiryMonth":"02",
   "expiryYear":"2019",
   "issueNumber":null,
   "billingAddress.city":"Wonderland",
   "billingAddress.code":"8796682911767",
   "billingAddress.firstname":"Raj Pawan",
   "billingAddress.lastname":"Gumdal",
   "billingAddress.line1":"Addr Line 1",
   "billingAddress.line2":null,
   "billingAddress.state":"US-AS",
   "billingAddress.region.isocode":"US-AS",
   "billingAddress.zip":"76767-6776"
}

服务器将接受这种转换格式的表单数据。

函数如下:

function jsonToFormData (inJSON, inTestJSON, inFormData, parentKey) {
    // http://stackoverflow.com/a/22783314/260665
    // Raj: Converts any nested JSON to formData.
    var form_data = inFormData || new FormData();
    var testJSON = inTestJSON || {};
    for ( var key in inJSON ) {
        // 1. If it is a recursion, then key has to be constructed like "parent.child" where parent JSON contains a child JSON
        // 2. Perform append data only if the value for key is not a JSON, recurse otherwise!
        var constructedKey = key;
        if (parentKey) {
            constructedKey = parentKey + "." + key;
        }

        var value = inJSON[key];
        if (value && value.constructor === {}.constructor) {
            // This is a JSON, we now need to recurse!
            jsonToFormData (value, testJSON, form_data, constructedKey);
        } else {
            form_data.append(constructedKey, inJSON[key]);
            testJSON[constructedKey] = inJSON[key];
        }
    }
    return form_data;
}

调用:

        var testJSON = {};
        var form_data = jsonToFormData (jsonForPost, testJSON);

我使用testJSON只是为了查看转换后的结果，因为我无法提取form_data的内容。AJAX post call:

        $.ajax({
            type: "POST",
            url: somePostURL,
            data: form_data,
            processData : false,
            contentType : false,
            success: function (data) {
            },
            error: function (e) {
            }
        });

抱歉这么晚才回答，我一直在纠结这个问题，因为Angular 2目前不支持文件上传。方法是用FormData发送一个XMLHttpRequest。我创建了一个函数来做这个。我用的是Typescript。要将其转换为Javascript只需删除数据类型声明。

/**
     * Transforms the json data into form data.
     *
     * Example:
     *
     * Input:
     * 
     * fd = new FormData();
     * dob = {
     *  name: 'phone',
     *  photos: ['myphoto.jpg', 'myotherphoto.png'],
     *  price: '615.99',
     *  color: {
     *      front: 'red',
     *      back: 'blue'
     *  },
     *  buttons: ['power', 'volup', 'voldown'],
     *  cameras: [{
     *      name: 'front',
     *      res: '5Mpx'
     *  },{
     *      name: 'back',
     *      res: '10Mpx'
     *  }]
     * };
     * Say we want to replace 'myotherphoto.png'. We'll have this 'fob'.
     * fob = {
     *  photos: [null, <File object>]
     * };
     * Say we want to wrap the object (Rails way):
     * p = 'product';
     *
     * Output:
     *
     * 'fd' object updated. Now it will have these key-values "<key>, <value>":
     *
     * product[name], phone
     * product[photos][], myphoto.jpg
     * product[photos][], <File object>
     * product[color][front], red
     * product[color][back], blue
     * product[buttons][], power
     * product[buttons][], volup
     * product[buttons][], voldown
     * product[cameras][][name], front
     * product[cameras][][res], 5Mpx
     * product[cameras][][name], back
     * product[cameras][][res], 10Mpx
     * 
     * @param {FormData}  fd  FormData object where items will be appended to.
     * @param {Object}    dob Data object where items will be read from.
     * @param {Object =   null} fob File object where items will override dob's.
     * @param {string =   ''} p Prefix. Useful for wrapping objects and necessary for internal use (as this is a recursive method).
     */
    append(fd: FormData, dob: Object, fob: Object = null, p: string = ''){
        let apnd = this.append;

        function isObj(dob, fob, p){
            if(typeof dob == "object"){
                if(!!dob && dob.constructor === Array){
                    p += '[]';
                    for(let i = 0; i < dob.length; i++){
                        let aux_fob = !!fob ? fob[i] : fob;
                        isObj(dob[i], aux_fob, p);
                    }
                } else {
                    apnd(fd, dob, fob, p);
                }
            } else {
                let value = !!fob ? fob : dob;
                fd.append(p, value);
            }
        }

        for(let prop in dob){
            let aux_p = p == '' ? prop : `${p}[${prop}]`;
            let aux_fob = !!fob ? fob[prop] : fob;
            isObj(dob[prop], aux_fob, aux_p);
        }
    }

你可以简单地使用:

formData.append('item', JSON.stringify(item));

该函数将object中的所有数据添加到FormData中

ES6版本来自@developer033:

function buildFormData(formData, data, parentKey) {
  if (data && typeof data === 'object' && !(data instanceof Date) && !(data instanceof File)) {
    Object.keys(data).forEach(key => {
      buildFormData(formData, data[key], parentKey ? `${parentKey}[${key}]` : key);
    });
  } else {
    const value = data == null ? '' : data;

    formData.append(parentKey, value);
  }
}

function jsonToFormData(data) {
  const formData = new FormData();
  
  buildFormData(formData, data);
  
  return formData;
}

const my_data = {
  num: 1,
  falseBool: false,
  trueBool: true,
  empty: '',
  und: undefined,
  nullable: null,
  date: new Date(),
  name: 'str',
  another_object: {
    name: 'my_name',
    value: 'whatever'
  },
  array: [
    {
      key1: {
        name: 'key1'
      }
    }
  ]
};

jsonToFormData(my_data)

jQuery版本:

function appendFormdata(FormData, data, name){
    name = name || '';
    if (typeof data === 'object'){
        $.each(data, function(index, value){
            if (name == ''){
                appendFormdata(FormData, value, index);
            } else {
                appendFormdata(FormData, value, name + '['+index+']');
            }
        })
    } else {
        FormData.append(name, data);
    }
}


var formData = new FormData(),
    your_object = {
        name: 'test object',
        another_object: {
            name: 'and other objects',
            value: 'whatever'
        }
    };
appendFormdata(formData, your_object); 

尝试 obj2fd=> https://www.npmjs.com/package/obj2fd

import obj2fd from 'obj2fd'

let data = {a:1, b:2, c:{ca:1}};
let dataWithFormData = obj2fd(data);
//result => [a=>1, b=>2, c=>[ca=>1]]