• Used bracket notation instead of dot notation (breaking change, but I don't think there are already projects that use this feature)
• Array-like objects will expand automatically. [] ending is not necessary.
• Added config.formSerializer: object config to handle rare cases:
  • indexes option to control flat arrays serialization:
    • null - don't add brackets (arr: 1, arr: 2, arr: 3)
    • false(default) - add empty brackets (arr[]: 1, arr[]: 2, arr[]: 3)
    • true - add brackets with indexes (arr[0]: 1, arr[1]: 2, arr[2]: 3)
  • metaTokens: boolean = true option to control the special ending (e.g user{}: '{"name": "John"}')
  • visitor: Function - user-defined visitor function that will be called recursively to serialize the data object
  • dots: boolean = false - use dot notation instead of brackets
• Added express.js/multer tests

The default config allows FormData to be processed by express.js out of the box;

const obj = {
  x: 1,
  arr: [1, 2, 3],
  arr2: [1, [2], 3],
  users: [{name: 'Peter', surname: 'Griffin'}, {name: 'Thomas', surname: 'Anderson'}],
  'obj2{}': [{x:1}]
};

The following steps will be executed by the Axios serializer internally:

const formData= new FormData();
formData.append('x', '1');
formData.append('arr[]', '1');
formData.append('arr[]', '2');
formData.append('arr[]', '3');
formData.append('arr2[0]', '1');
formData.append('arr2[1][0]', '2');
formData.append('arr2[2]', '3');
formData.append('users[0][name]', 'Peter');
formData.append('users[0][surname]', 'Griffin');
formData.append('users[1][name]', 'Thomas');
formData.append('users[1][surname]', 'Anderson');
formData.append('obj2{}', '[{"x":1}]');

Closes #4698