Feature/control draggability of individual points

[rendertom]

User story:
As a user I want to have control over the draggability of particular set of selected points without modifying the initial selection.

Description:
This PR exposes additional API for the developer to change the draggability option for a set of particular points.

• canBeDragged(element): checks whether the element can be dragged.
• makeDraggable(element): make element draggable.
• makeNonDraggable(element): make element non-draggable.

Usage example:

const ds = new DragSelect({
  selectables: document.getElementsByClassName('item'),
  area: document.getElementById('container'),
  draggability: true, // optional, but has to be set 'true' to control draggability of individual points
  noDragClass: 'no-drag', // optional, defaults to 'ds-no-drag'
});

// Make every other element non-draggable
ds.subscribe('predragstart', (data) => {
  if (data.isDragging) {
    data.items.forEach((item, index) => {
      index % 2 === 0 // index is even
        ? ds.makeDraggable(item)
        : ds.makeNonDraggable(item);
    });
  }
});

[ThibaultJanBeyer]

Thank you for your contribution @rendertom! This makes sense! 🎉

I left a few comments and would ask you to also do following:

• Add a test for this (check other tests to see how it's done, it's very simple)
• Add the information to the online docs in the www folder
• Merge latest master

Then I'll merge! Thank you!!

[ThibaultJanBeyer]

I guess the description is wrong

[ThibaultJanBeyer]

maybe rename to isDraggable. Which is clearer that it's a question than a setter.

[ThibaultJanBeyer]

Hmm can you clarify this? As of now then if I turn draggability off in the settings, all elements should have this class, right? Maybe think about a more precise description 🤔

[ThibaultJanBeyer]

Hey there, I’m visiting this as part of v3. I’ll only take over the class, then, as a developer, I can just add/remove the class to whatever element whenever I want which in turn stops the dragging on an individual element, I think that’s quite cool! Closing for now, expect to see it in v3

Edit: or actually what do you think about a custom filter override? Like we have for filterSelected (docs)? I.e. a filterDragElements override… I tend to prefer that approach because, sure it’s slightly more complex, but it gives users the full power of control 🤔