fix memory leak within debug instance

Author: Qix-

src/common.js

@@ -17,11 +17,6 @@ function setup(env) {
 		createDebug[key] = env[key];
 	});
 
-	/**
-	* Active `debug` instances.
-	*/
-	createDebug.instances = [];
-
 	/**
 	* The currently active debug mode names, and names to skip.
 	*/
@@ -63,6 +58,7 @@ function setup(env) {
 	*/
 	function createDebug(namespace) {
 		let prevTime;
+		let enableOverride = null;
 
 		function debug(...args) {
 			// Disabled?
@@ -115,31 +111,27 @@ function setup(env) {
 		}
 
 		debug.namespace = namespace;
-		debug.enabled = createDebug.enabled(namespace);
 		debug.useColors = createDebug.useColors();
 		debug.color = createDebug.selectColor(namespace);
-		debug.destroy = destroy;
 		debug.extend = extend;
 
+		Object.defineProperty(debug, 'enabled', {
+			enumerable: true,
+			configurable: false,
+			get: () => enableOverride === null ? createDebug.enabled(namespace) : enableOverride,
+			set: v => {
+				enableOverride = v;
+			}
+		});
+
 		// Env-specific initialization logic for debug instances
 		if (typeof createDebug.init === 'function') {
 			createDebug.init(debug);
 		}
 
-		createDebug.instances.push(debug);
-
 		return debug;
 	}
 
-	function destroy() {
-		const index = createDebug.instances.indexOf(this);
-		if (index !== -1) {
-			createDebug.instances.splice(index, 1);
-			return true;
-		}
-		return false;
-	}
-
 	function extend(namespace, delimiter) {
 		const newDebug = createDebug(this.namespace + (typeof delimiter === 'undefined' ? ':' : delimiter) + namespace);
 		newDebug.log = this.log;
@@ -177,11 +169,6 @@ function setup(env) {
 				createDebug.names.push(new RegExp('^' + namespaces + '$'));
 			}
 		}
-
-		for (i = 0; i < createDebug.instances.length; i++) {
-			const instance = createDebug.instances[i];
-			instance.enabled = createDebug.enabled(instance.namespace);
-		}
 	}
 
 	/**