Convert object data into FormData

createFormData.js

function createFormData(data, previousKey, formData = new FormData()) {
  if (isPlainObject(data)) {
    Object.keys(data).forEach(key => {
      const value = data[key];
      let newKey = key;

      if (isPlainObject(value)) {
        return createFormData(value, key, formData);
      }

      if (previousKey) {
        newKey = `${previousKey}[${key}]`;
      }

      if (isArray(value)) {
        value.forEach((item, index) => {
          if (isPlainObject(item)) {
            createFormData(item, `${newKey}[${index}]`, formData);
          } else {
            formData.append(`${newKey}[${index}]`, item);
          }
        });
      } else {
        formData.append(newKey, value);
      }
    });
  } else if (previousKey) {
    formData.append(previousKey, data);
  }

  return formData;
}

example.js

const input = require('./input.json');

console.log(createFormData(input));

input.json

{
    "title": "A Title",
    "body": "Some details",
    "images": [
        {
            "name": "C0A5A8EA-6935-4148-B166-33FD198F6672.jpg",
            "type": "image/jpeg",
            "uri": "/Users/alexmccabe/Library/Developer/CoreSimulator/Devices/71642DC3-655E-485A-BA3F-DC32FB7D3C55/data/Containers/Data/Application/22091589-91C7-4593-8323-F7AA0F725FB0/tmp/react-native-image-crop-picker/C0A5A8EA-6935-4148-B166-33FD198F6672.jpg"
        },
        {
            "name": "2A632728-3BA9-466E-9732-417D74304674.jpg",
            "type": "image/jpeg",
            "uri": "/Users/alexmccabe/Library/Developer/CoreSimulator/Devices/71642DC3-655E-485A-BA3F-DC32FB7D3C55/data/Containers/Data/Application/22091589-91C7-4593-8323-F7AA0F725FB0/tmp/react-native-image-crop-picker/2A632728-3BA9-466E-9732-417D74304674.jpg"
        }
    ],
    "categoryId": 1,
    "tags": [
        {
            "id": 8,
            "type": "genre",
            "name": "2-Tone"
        },
        {
            "id": 11,
            "type": "genre",
            "name": "8-Bit / BitPop"
        },
        {
            "id": 13,
            "type": "genre",
            "name": "Acid Breaks"
        }
    ]
}

output.json

{
    "_parts": [
        [
            "title",
            "A Title"
        ],
        [
            "body",
            "Some details"
        ],
        [
            "images[0][name]",
            "C0A5A8EA-6935-4148-B166-33FD198F6672.jpg"
        ],
        [
            "images[0][type]",
            "image/jpeg"
        ],
        [
            "images[0][uri]",
            "/Users/alexmccabe/Library/Developer/CoreSimulator/Devices/71642DC3-655E-485A-BA3F-DC32FB7D3C55/data/Containers/Data/Application/22091589-91C7-4593-8323-F7AA0F725FB0/tmp/react-native-image-crop-picker/C0A5A8EA-6935-4148-B166-33FD198F6672.jpg"
        ],
        [
            "images[1][name]",
            "2A632728-3BA9-466E-9732-417D74304674.jpg"
        ],
        [
            "images[1][type]",
            "image/jpeg"
        ],
        [
            "images[1][uri]",
            "/Users/alexmccabe/Library/Developer/CoreSimulator/Devices/71642DC3-655E-485A-BA3F-DC32FB7D3C55/data/Containers/Data/Application/22091589-91C7-4593-8323-F7AA0F725FB0/tmp/react-native-image-crop-picker/2A632728-3BA9-466E-9732-417D74304674.jpg"
        ],
        [
            "category_id",
            1
        ],
        [
            "tag_ids[0]",
            8
        ],
        [
            "tag_ids[1]",
            11
        ],
        [
            "tag_ids[2]",
            13
        ]
    ]
}