Get object from array inputs - native way to serialize a form

form.html

<form>
  <label for="name">Name</label>
  <input type="text" name="user[name]" id="name">

  <label for="email">Email</label>
  <input type="email" name="user[email]" id="email">

  <label for="description">Description</label>
  <textarea name="user[description]" id="description"></textarea>

  <label for="password">Password</label>
  <input type="password" name="user[password]" id="password">

  <input type="submit" value="Submit">
</form>

form.js

var user, fields;

user = {};
fields = document.querySelectorAll('input[name^=user], textarea[name^=user]');

for (var i = 0, length = fields.length; i < length; i++) {
  var field, name, attr;

  field = fields[i];
  name = field.name;
  attr = name.substring(name.lastIndexOf('[') + 1, name.lastIndexOf(']'));

  user[attr] = field.value;
};

// user = {
//   email: "[email protected]",
//   name: "Thiago Henrique Poiani",
//   description: "",
//   password: "UrP7AnI55x9bVo9"
// }

Change this:

fields = document.querySelectorAll('input[name^=user], textarea[name^=user]');

for this:

fields = document.querySelectorAll('[name^=user]');