cache enabled status per-logger (#799)

Co-authored-by: Qix <[email protected]>

src/common.js

@@ -60,6 +60,8 @@ function setup(env) {
 	function createDebug(namespace) {
 		let prevTime;
 		let enableOverride = null;
+		let namespacesCache;
+		let enabledCache;
 
 		function debug(...args) {
 			// Disabled?
@@ -120,7 +122,17 @@ function setup(env) {
 		Object.defineProperty(debug, 'enabled', {
 			enumerable: true,
 			configurable: false,
-			get: () => enableOverride === null ? createDebug.enabled(namespace) : enableOverride,
+			get: () => {
+				if (enableOverride !== null) {
+					return enableOverride;
+				}
+				if (namespacesCache !== createDebug.namespaces) {
+					namespacesCache = createDebug.namespaces;
+					enabledCache = createDebug.enabled(namespace);
+				}
+
+				return enabledCache;
+			},
 			set: v => {
 				enableOverride = v;
 			}
@@ -149,6 +161,7 @@ function setup(env) {
 	*/
 	function enable(namespaces) {
 		createDebug.save(namespaces);
+		createDebug.namespaces = namespaces;
 
 		createDebug.names = [];
 		createDebug.skips = [];