max / quasi

3.0 KB · 74 lines History Blame Raw

1	// Putting a described value on the clipboard.
2	//
3	// `c3e145e0`. An `Act` can say that pressing it copies a value, and this is the
4	// browser's half. It replaces seven `window.<name>` globals across 14 sites on
5	// the MNW server, six of which scraped the text back off the DOM at press time
6	// and one of which read an element by id.
7	//
8	// It reads one attribute the node emitter writes and nothing else:
9	// `data-copies` carries the value. An ordinary escaped attribute, so nothing
10	// here is a program built out of app text -- the same rule that makes this a
11	// script rather than an emitted _hyperscript program. A licence key reading
12	// `"; alert(1); "` is a value in an attribute here and could not be one in a
13	// program.
14	//
15	// What it does NOT do is say "Copied!". Every shipped site relabelled its own
16	// button and reverted, six at 1500ms and one at 2000ms, and that is a temporary
17	// label rather than a copy: it belongs to `makeover-timing` and to mnw-server
18	// `033c722f`. Splitting them is deliberate -- a host with no notion of a
19	// reverting label still needs to be told the act copies something.
20	(() => {
21	"use strict";
22
23	/** The value to put on the clipboard. */
24	const VALUE = "data-copies";
25
26	/**
27	* Write `text` to the clipboard, preferring the async API.
28	*
29	* `navigator.clipboard` is unavailable on an insecure origin and can be
30	* refused by permissions policy, and neither is an error worth surfacing to
31	* a reader who pressed a copy button. The fallback is the old selection
32	* dance, which works in both cases and is why it is still here.
33	*/
34	const write = async (text) => {
35	try {
36	if (navigator.clipboard?.writeText) {
37	await navigator.clipboard.writeText(text);
38	return;
39	}
40	} catch {
41	// Fall through: refused, or no permission. The fallback below does
42	// not ask for one.
43	}
44
45	const carrier = document.createElement("textarea");
46	carrier.value = text;
47	// Off-screen rather than hidden: a `display: none` element cannot be
48	// selected, and selecting is the whole mechanism here.
49	carrier.setAttribute("readonly", "");
50	carrier.style.position = "fixed";
51	carrier.style.top = "-9999px";
52	document.body.appendChild(carrier);
53	carrier.select();
54	try {
55	document.execCommand("copy");
56	} catch {
57	// Nothing left to try. The reader sees no change, which is the
58	// same outcome as a page that never described the copy at all.
59	}
60	carrier.remove();
61	};
62
63	// One delegated listener rather than one per control, for `FILL_JS`'
64	// reason: these controls arrive in swaps, so binding per element would mean
65	// rebinding on every swap.
66	document.addEventListener("click", (event) => {
67	const control = event.target?.closest?.(`[${VALUE}]`);
68	if (!control) {
69	return;
70	}
71	void write(control.getAttribute(VALUE) ?? "");
72	});
73	})();
74