Droppable doesn't work if used on an element with `display: contents`

[connoratmyxt]

Hi, I found this bug while using your library. I am willing to create a PR to fix this if you'd like.

Steps to reproduce

1. Use display: contents on an element
2. Make a Droppable with it
3. It doesn't work (the Droppable only uses the bounding box of the container to calculate the droppable area, which is always [0,0,0,0] on elements with display: contents)

Expected behavior

If the bounding box is [0,0,0,0], the Droppable should use the union of the bounding boxes of any not-absolutely-positioned children as the droppable area.

Code

This code doesn't work

import agnosticDraggable from "https://cdn.skypack.dev/agnostic-draggable@1.4.3";
const { Draggable, Droppable } = agnosticDraggable

const app = document.createElement("div")

const data = [
	{ name: "foo", number: 100, date: new Date(Date.now() - 2 * 60 * 1000).toLocaleString() },
	{ name: "bar", number: 200, date: new Date(Date.now() - 60 * 1000).toLocaleString() },
	{ name: "baz", number: 300, date: new Date(Date.now()).toLocaleString() }
]

const table = document.createElement("table")
table.style.width = "calc(100% - 40px)"
table.style.margin = "20px"
table.style.display = "grid"
table.style.gridTemplateColumns = "auto auto auto"
const thead = document.createElement("thead")
thead.style.display = "contents"
const tbody = document.createElement("tbody")
tbody.style.display = "contents"

const tr = document.createElement("tr")
tr.style.display = "contents"
for (const col of Object.keys(data[0])) {
	const th = document.createElement("th")
	th.style.background = "rgba(127, 127, 127, .1)"
	th.style.padding = "8px"
	th.style.border = "solid rgb(127,127,127)"
	th.style.borderWidth = "1px 0"
	th.textContent = col
	tr.appendChild(th)
}
thead.appendChild(tr)

for (const row of data) {
	const tr = document.createElement("tr")
	tr.style.display = "contents"
	const cells = Object.values(row).map((cell) => {
		const td = document.createElement("td")
		td.style.padding = "8px"
		td.style.border = "solid rgb(127,127,127)"
		td.style.borderWidth = "1px 0"
		td.textContent = cell
		tr.appendChild(td)
	})
	tbody.appendChild(tr)

	new Droppable(
		tr,
		{
			tolerance: "pointer",
		},
		{
			"droppable:over": () => {
				tr.style.background = "blue"
			},
			"droppable:out": () => {
				tr.style.background = ""
			},
			"droppable:drop": () => {
				tr.style.background = ""
				const td = tr.querySelector("td:nth-child(2)")
				td.textContent = parseInt(td.textContent) + 1
			}
		}
	)
}

table.appendChild(thead)
table.appendChild(tbody)
app.appendChild(table)

const addDiv = document.createElement("div")
addDiv.style.display = "inline-block"
addDiv.style.margin = "20px"
addDiv.style.padding = "8px"
addDiv.style.background = "rgb(127,127,127)"
addDiv.textContent = "Drop me on a row to add 1"

app.appendChild(addDiv)

document.body.appendChild(app)

let listener = (e) => {
	e.preventDefault()
}
new Draggable(
	addDiv,
	{
		revert: true,
	},
	{
		"drag:start": () => {
			document.body.addEventListener("selectstart", listener)
		},
		"drag:stop": () => {
			document.body.removeEventListener("selectstart", listener)
		}
	}
)

This code works

import agnosticDraggable from "https://cdn.skypack.dev/agnostic-draggable@1.4.3";
const { Draggable, Droppable } = agnosticDraggable

const app = document.createElement("div")

const data = [
	{ name: "foo", number: 100, date: new Date(Date.now() - 2 * 60 * 1000).toLocaleString() },
	{ name: "bar", number: 200, date: new Date(Date.now() - 60 * 1000).toLocaleString() },
	{ name: "baz", number: 300, date: new Date(Date.now()).toLocaleString() }
]

const table = document.createElement("table")
table.style.width = "calc(100% - 40px)"
table.style.margin = "20px"
const thead = document.createElement("thead")
const tbody = document.createElement("tbody")

const tr = document.createElement("tr")
for (const col of Object.keys(data[0])) {
	const th = document.createElement("th")
	th.style.background = "rgba(127, 127, 127, .1)"
	th.style.padding = "8px"
	th.style.border = "solid rgb(127,127,127)"
	th.style.borderWidth = "1px 0"
	th.textContent = col
	tr.appendChild(th)
}
thead.appendChild(tr)

for (const row of data) {
	const tr = document.createElement("tr")
	const cells = Object.values(row).map((cell) => {
		const td = document.createElement("td")
		td.style.padding = "8px"
		td.style.border = "solid rgb(127,127,127)"
		td.style.borderWidth = "1px 0"
		td.textContent = cell
		tr.appendChild(td)
	})
	tbody.appendChild(tr)

	new Droppable(
		tr,
		{
			tolerance: "pointer",
		},
		{
			"droppable:over": () => {
				tr.style.background = "blue"
			},
			"droppable:out": () => {
				tr.style.background = ""
			},
			"droppable:drop": () => {
				tr.style.background = ""
				const td = tr.querySelector("td:nth-child(2)")
				td.textContent = parseInt(td.textContent) + 1
			}
		}
	)
}

table.appendChild(thead)
table.appendChild(tbody)
app.appendChild(table)

const addDiv = document.createElement("div")
addDiv.style.display = "inline-block"
addDiv.style.margin = "20px"
addDiv.style.padding = "8px"
addDiv.style.background = "rgb(127,127,127)"
addDiv.textContent = "Drop me on a row to add 1"

app.appendChild(addDiv)

document.body.appendChild(app)

let listener = (e) => {
	e.preventDefault()
}
new Draggable(
	addDiv,
	{
		revert: true,
	},
	{
		"drag:start": () => {
			document.body.addEventListener("selectstart", listener)
		},
		"drag:stop": () => {
			document.body.removeEventListener("selectstart", listener)
		}
	}
)

Suggested solution

1. If the Droppable element has a bounding box of [0,0,0,0], search deeply for any children (excluding position: absolute or position: fixed) that have a not-zero bounding box
2. Use those bounding boxes to test whether a Draggable is over the Droppable

[marcospont]

Hi, @connoratmyxt

I will try to come up with a solution based on your suggestion.

Thanks for the detailed information!