Have the ability to cancel a delete

[biscuit314]

When the user clicks the "delete a node" button, sometimes we need to check first before completing the deletion. For example:

• pop an "are you sure?" to give the user a chance to back out if she clicked delete in error
• in the event deleting the backing item in a database or API fails

To allow for this, this feature request is for a new event treeNodeBeforeDelete which allows the application to perform the check then indicate whether the delete should be allowed to continue. For example:

<tree-view ... @treeNodeBeforeDelete="onBeforeDelete" ...>
...
function onBeforeDelete(target) {
    const answer = askAreYouSure()  // prompts user, returns boolean
    return answer
}

// OR
function onBeforeDelete(target) {
    const answer = askAreYouSure()
    if (answer === false) {
        target.cancelDeletion()  // or some other manipulation of the target node
    }
}

[grapoza]

@biscuit314 I'll probably merge this after the weekend, so if you get a chance to take a look and/or try out the solution let me know. I added a deleteNodeCallback property for the treeNodeSpec that gets called when the delete button is clicked and can return a boolean indicating whether to continue with deletion. If you checkout the source and run yarn storybook there's an Add Remove example with a very lazy Promise.resolve(window.confirm... implementation that should give you the gist of it.

[biscuit314]

This is fantastic. I'll give it a try this week and let you know if I find anything!