formData.js

// manage json objects to js form data

const formData = (obj) => {
	let data = new FormData();

	for (var key in obj){
		if (!obj.hasOwnProperty(key)) { continue; }

		let item = obj[key];

		if (typeof item === 'undefined'){ continue; }

		if (typeof item === 'object' && item.length){
			for (var i = 0; i < item.length; i += 1){
				data.append(key + '[]', item[i]);
			}
			continue;
		}

		if (typeof item === 'object'){
			for (var item_key in item){
				if (!obj.hasOwnProperty(key)) { continue; }

				data.append(key + '_' + item_key, item[item_key]);
			}

			continue;
		}

		data.append(key, item);
	}
	return data;
}