fix: Fix exactOptionalPropertyTypes (#20)

This makes this work correctly when exactOptionalPropertyTypes is set to
true.

package.json

@@ -4,9 +4,6 @@
   "version": "5.1.0",
   "repository": "github:rocicorp/logger",
   "license": "Apache-2.0",
-  "engines": {
-    "node": "^14.13.1 || >=16.0.0"
-  },
   "scripts": {
     "test": "mocha --ui=tdd out/*.test.js",
     "pretest": "npm run build",
@@ -27,7 +24,7 @@
     "mocha": "^9.2.2",
     "prettier": "^2.6.0",
     "sinon": "^13.0.1",
-    "typescript": "^4.6.2"
+    "typescript": "^5.1.3"
   },
   "type": "module",
   "types": "out/logger.d.ts",

src/logger.ts

@@ -6,10 +6,10 @@
  * only [[error]] will be present.
  */
 export interface OptionalLogger {
-  error?(...args: unknown[]): void;
-  info?(...args: unknown[]): void;
-  debug?(...args: unknown[]): void;
-  flush?(): Promise<void>;
+  error?: ((...args: unknown[]) => void) | undefined;
+  info?: ((...args: unknown[]) => void) | undefined;
+  debug?: ((...args: unknown[]) => void) | undefined;
+  flush?: (() => Promise<void>) | undefined;
 }
 
 /**
@@ -57,9 +57,9 @@ export class TeeLogSink implements LogSink {
 }
 
 export class OptionalLoggerImpl implements OptionalLogger {
-  readonly debug?: (...args: unknown[]) => void = undefined;
-  readonly info?: (...args: unknown[]) => void = undefined;
-  readonly error?: (...args: unknown[]) => void = undefined;
+  readonly debug?: ((...args: unknown[]) => void) | undefined = undefined;
+  readonly info?: ((...args: unknown[]) => void) | undefined = undefined;
+  readonly error?: ((...args: unknown[]) => void) | undefined = undefined;
   readonly flush: () => Promise<void>;
 
   constructor(logSink: LogSink, level: LogLevel = 'info', context?: Context) {

tsconfig.json

@@ -9,12 +9,10 @@
     "noImplicitReturns": true,
     "noFallthroughCasesInSwitch": true,
     "esModuleInterop": true,
-
-    "importsNotUsedAsValues": "error",
-
+    "exactOptionalPropertyTypes": true,
     "declaration": true,
     "forceConsistentCasingInFileNames": true,
-    "moduleResolution": "node",
+    "moduleResolution": "node16",
     "outDir": "out",
     "allowJs": true,
     // esnext for Object.fromEntries