Deduplicate active plugin list when using 'add' option

.changeset/green-cameras-invent.md

@@ -0,0 +1,5 @@
+---
+"eleventy-plugin-embed-everything": patch
+---
+
+Deduplicate list of active plugins when using the 'add' option

packages/everything/lib/configOptions.js

@@ -21,8 +21,9 @@ module.exports = function(options = {}) {
 function setActivePlugins(obj) {
 	let active = [...defaultPlugins]; // default
 	// Add to default plugin list
+	// The `Set` ensures there are no duplicates
 	if (obj.add) {
-		active = [...defaultPlugins, ...obj.add];
+		active = [...new Set([...defaultPlugins, ...obj.add])];
 	}
 	// Define custom plugin list from scratch.
 	// Will always override `add`

packages/everything/test/test-configOptions.js

@@ -70,6 +70,17 @@ test(
 	},
 );
 
+test(
+	`Config "add" option returns deduplicated output when adding plugins already included by default`,
+	(t) => {
+		let output = config({
+			// These are already active by default, so `add`ing should do nothing
+			add: ["youtube", "vimeo"],
+		});
+		t.deepEqual(output, defaultOptions);
+	},
+)
+
 test(
 	`Config returns expected output with valid "use" option`,
 	(t) => {