wip: add form controller

[43081j]

playing around with introducing a form controller.

with this kind of usage:

const initialValue = {foo: 'bar'};
const ctrl = new FormController(this, initialValue);

html`
  <form ${ctrl.attach()}>
    <label>
      Email:
      <input ${ctrl.bind('email')}>
    </label>
    <label>
      Password:
      <input type="password" ${ctrl.bind('password')}>
    </label>
  </form>
`;

you can also use validators:

• form validators run on submission after user input has updated the model
• field validators run on user input before user input updates the model (and can prevent it)

ctrl.addValidator((values) => {
  // values here is `ctrl.value`
  // this will be called on submission and decide if the form should submit or not
});

ctrl.addValidator(('email', (value) => {
  // value here is the email from `ctrll.value.email`
  // returning a string here will imply the field is invalid and will add the string to `ctrl.errors`
  // returning void or null will imply the field is valid
});

draft until it becomes less of an endless what if?

[coveralls]

Pull Request Test Coverage Report for Build 4660014813

• 251 of 251 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 98.565%

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Totals
Change from base Build 4420305954:	0.3%
Covered Lines:	2326
Relevant Lines:	2345

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💛 - Coveralls

[43081j]

we should add:

• validation of some sort
• automatic handling of submissions (just listen to the submit event and expose some kind of submit handler, but also provide some kind of endpoint for the common cases)
• expose validation errors on ctrl.errors

[43081j]

still perfecting this but now we're getting somewhere:

// snipped - see next post

to figure out:

basically the form validators don't work right now. they get passed the entire object but before any changes from the user input happened (making them useless).

validators are meant to prevent input from updating the value if they return falsely.

so either we throw away 'form validators' and stick with just field validators, or we create a deep clone of the value just to give these validators (so they can still prevent changes).

not sure yet...

[43081j]

ok new update:

• form validators run on submission after user input has updated the model
• field validators run on user input before user input updates the model (and can prevent it)

so updated usage:

ctrl.addValidator((values) => {
  // values here is `ctrl.value`
  // this will be called on submission and decide if the form should submit or not
});

ctrl.addValidator(('email', (value) => {
  // value here is the email from `ctrll.value.email`
  // returning a string here will imply the field is invalid and will add the string to `ctrl.errors`
  // returning void or null will imply the field is valid
});