Add before callback to form link

[condef5]

This pr adds a callback to the form link that is executed in convertLinkWithMethodClickToFormSubmission.

With this callback we could add some custom behavior like this:

Turbo.setLinkToFormBeforeCallback((form) => {
  if (form.getAttribute('method') !== 'delete') return;
  
  const input = document.createElement("input");
  input.setAttribute("name", "_method")
  input.setAttribute("type", "hidden")
  input.setAttribute("value", "delete")
  
  form.method = 'post'
  form.appendChild(input)
})

This little script converts the links with the delete method to post and also adds a _method field with a delete value in the form link.

Notes:

1. We also could add this script to turbo-rails in order to fix this "data-turbo-method: delete" should use POST with _method rather than DELETE turbo-rails#259
2. I'm open to suggestions to find a better name 😅

[dhh]

Given that this really is just to be used for the specific case of using _method field with delete for Rails, I think we should just bake that implementation in, exposed a flag to flip that setting, ala Turbo.encodeHiddenLinkFormMethod = true, which turbo-rails can then trigger. Other frameworks may indeed want to follow suit on this.

[seanpdoyle]

Could turbo-rails support this directly, with an event listener like the one introduced in https://github.com/hotwired/turbo-rails/pull/239/files#diff-f438134433fd9897751d1b5cd219ea33ac29be8f3af3e4ac17e65475e4cadbeeR1-R7?

[brunoprietog]

Hi @condef5, Thanks for the proposal, but I'm closing this for now. It's possible to do something similar with event listeners as well.