Improved FormData support;

[DigitalBrainJS]

CODE

• Fixed isFormData predicate;
• Added form-data as a dependency for node.js build only. It is used by default to handle the FormData payload;
• Added shortcut methods postForm, putForm, patchForm
• Reworked toFormData serializer;
  • ArrayBuffer and/or TypedArray will be converted to a Blob|Buffer instance
  • Added support for special field endings:
    • [] - unwrap the array like object as separate fields with the same key
    • {} - serialize the value with JSON.stringify

axios.postForm('https://httpbin.org/post', {
  'myObj{}': {x: 1, s: "foo"},
  'files[]': document.querySelector('#fileInput').files 
};

• You can pass the FileList object directly as the payload:

await axios.postForm('https://httpbin.org/post', document.querySelector('#fileInput').files)

• Exposed toFormData helper as a static method;
• Added kindOf, kindOfTest, endsWith, isTypedArray util;

TESTS

• Added test for Fixed isFormData predicate; #4413;
• Added test for automatic data object serialization to a FormData payload when the request Content-Type is multipart/form-data;
• Added backend test for passing FormData as a payload;

README

• Added FormData automatic serialization section to Readme.md;
• Updated cancellation section;

DEV

• Added cross-env package to run the build scripts on Windows systems;
• Added formidable to test FormData payload;

[carpben]

Added tests are excellent and valuable 🙌.

At present I suggest we don't recommend auto-serialization of form-data as the default method of choice. Instead, let's move it to be after the manual section and say that we support it now. After we have more tests, and after it is well accepted by the community, let's adapt and recommend it by default.
Currently, conversion of files in node will not work. This is solved by #4469 but tests and feedback are needed in this area.

This Pr goes way beyond adding tests to FormData payload as the title suggest. It includes FormData documentation, a whole section of documentation about AbortController, adding import from "form-data" to "Node" only, and what seems like unrelated changes to scripts (cross-env). I guess it is obvious why this is less than ideal.
While the contribution is great it would be even better if it will be separated to PRs that are scoped to a certain topic/domain.

[jasonsaayman]

@DigitalBrainJS can you have a look at the review please?

[dtrucken]

Question: is there a way to send a multipart PUT with a value other than what gets hard-coded in lib/core/Axios.js line 184
'Content-Type': 'multipart/form-data'

In versions of axis 0.26.x and earlier, I could change that to what my 3rd-party server requires: 'multipart/mixed', but now I can not. I would like to use the 1.x.x version to get past all the security issues flagged in earlier versions.