How Does Trello Access the User's Clipboard

How does Trello access the user's clipboard?

Disclosure: I wrote the code that Trello uses; the code below is the actual source code Trello uses to accomplish the clipboard trick.

---

We don't actually "access the user's clipboard", instead we help the user out a bit by selecting something useful when they press Ctrl+C.

Sounds like you've figured it out; we take advantage of the fact that when you want to hit Ctrl+C, you have to hit the Ctrl key first. When the Ctrl key is pressed, we pop in a textarea that contains the text we want to end up on the clipboard, and select all the text in it, so the selection is all set when the C key is hit. (Then we hide the textarea when the Ctrl key comes up.)

Specifically, Trello does this:

TrelloClipboard = new class
  constructor: ->
    @value = ""

    $(document).keydown (e) =>
      # Only do this if there's something to be put on the clipboard, and it
      # looks like they're starting a copy shortcut
      if !@value || !(e.ctrlKey || e.metaKey)
        return

      if $(e.target).is("input:visible,textarea:visible")
        return

      # Abort if it looks like they've selected some text (maybe they're trying
      # to copy out a bit of the description or something)
      if window.getSelection?()?.toString()
        return

      if document.selection?.createRange().text
        return

      _.defer =>
        $clipboardContainer = $("#clipboard-container")
        $clipboardContainer.empty().show()
        $("<textarea id='clipboard'></textarea>")
        .val(@value)
        .appendTo($clipboardContainer)
        .focus()
        .select()

    $(document).keyup (e) ->
      if $(e.target).is("#clipboard")
        $("#clipboard-container").empty().hide()

  set: (@value) ->

In the DOM we've got:

<div id="clipboard-container"><textarea id="clipboard"></textarea></div>

CSS for the clipboard stuff:

#clipboard-container {
  position: fixed;
  left: 0px;
  top: 0px;
  width: 0px;
  height: 0px;
  z-index: 100;
  display: none;
  opacity: 0;
}
#clipboard {
  width: 1px;
  height: 1px;
  padding: 0px;
}

... and the CSS makes it so you can't actually see the textarea when it pops in ... but it's "visible" enough to copy from.

When you hover over a card, it calls

TrelloClipboard.set(cardUrl)

... so then the clipboard helper knows what to select when the Ctrl key is pressed.

Does Trello provide a way to identify who created a card?

You can find the author of the card using actions, like this:

Trello.get('/cards/CARD_ID_HERE/actions?action_memberCreator_fields')

It is under the arguments for GET /1/cards/[card id or shortlink] here: https://developers.trello.com/advanced-reference/card#get-1-cards-card-id-or-shortlink

You can also get a list of all your cards like this:

Trello.get('/members/me/cards')

and use the field idBoard to filter only cards for specific board.

How does Trello handle rearrangement of cards, lists, checklists etc

Each item is given a pos (a JavaScript number, so double-precision float). Then, they are rendered by sorting by pos.

When a new item is added, it's pos is based on where in the list it is:

• bottom of list - maximum pos currently in the list + a buffer (I think 1024 is used)
• top of list - minimum pos currently in the list divided by two
• middle of list - average of pos of the two adjacent items

The middle option would be assigned by the client; the top/bottom can either be assigned by the client or passed to the server as the strings "top" or "bottom" in which case the server will perform the logic.

On the server, after assigning the pos to the new item as shown above, the item is checked against its nearest neighbors for adjacency - if they are less than a minimum distance apart (.01 is used, I believe), they are spread out (potentially cascading into increasing the pos of the entire list).

I don't think this is the ideal way, but it is how Trello does it.

How to access the trello API from within a powerup?

Since your power-up is run through an iframe, it's not actually coming from the Trello page itself so you need to specify your API key and token in the GET URL.

Example:

https://api.trello.com/1/boards/560bf4298b3dda300c18d09c?fields=name,url&key={YOUR-API-KEY}&token={AN-OAUTH-TOKEN}

The info for getting your API key and token can be found here: https://trello.readme.io/v1.0/reference#api-key-tokens

---

Related Topics