Submitting a form using GET: discrepancy between htmx and browser

[ergor]

Description

Given this form:

<form action="/test" method="get">
  <input type="hidden" name="action" value="A">
  <button id="btnB" type="submit" name="action" value="B">B</button>
</form>

When clicking the button,
The browser's behavior is to append both values, resulting in a query string as "action=A&action=B".

But, when using HTMX, given this form:

<form hx-get="/test">
  <input type="hidden" name="action" value="A">
  <button id="btnB" type="submit" name="action" value="B">B</button>
</form>

When clicking the button,
HTMX issues a GET request, where the button's value overrides any other form data with the same name; the resulting query string is just "action=B". This is unexpected behavior.

This patch tries to bring HTMX in line with default browser behavior.

Now, I think this solution is rather hacky. Why is there differentiation between GET and non-GET requests in getInputValues() in the first place? I don't know the intricacies of HTMX, explanations are appreciated. I am open to iterate on this PR if the solution is below quality expectation.

Corresponding issue:
#1541
This issue brought it up, but was then closed due to #1559. However, that PR didn't fix it for the case of GET.

Testing

I tested it using the test suite. I added relevant test-cases that triggered the bug, and then verified the fix by running the tests with npm run test

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded