add custom node filter to `generateFormElements`

[allenfantasy]

First thanks for this brilliant library 👍

Here I use the generateFormElements method to create form elements before submitting the selected nodes. However I found that I don't need to submit unselectable nodes since they are locked and user shouldn't update them.

Also I found the generateFormElements have used getSelectedNodes where it picks up only selected nodes - but I would like to picked up partsel nodes as well and exclude all unselectable nodes.

Sure I could hack the original source code the achieve this but I think it's better to raise the issue here to hear your advice first :)

So here it goes:

Expected behavior

Enable user customize the returned nodes in generateFormElements. IMHO it could be achieved by either way:

• Providing a configurable option in FancytreeOptions
• Providing a configurable option when calling the generateFormElements method.

Environment

• Browser type and version: Chrome 50.0.2661.86 (64-bit)
• jQuery and jQuery UI versions: 1.12.3 / 1.11.4
• Fancytree version: 2.17.1
• enabled/affected extensions: table, dnd enabled

[mar10]

generateFormElements() already has an optsargument. We could add an additional option (e.g. otps.filter) that accepts a callback function.

If specified, tree.generateFormElements() would use visit()instead of getSelectedNodes(), call filter(node), and serializes all nodes that we return true for?

[allenfantasy]

Thank you for your reply :)

Yes - I think the addition option could be opts.filter and if opts.filter is defined we use visit() to call filter(node) to return wanted nodes.

[mar10]

(see also #310)