isLogLevel() function

CHANGES.md

@@ -9,6 +9,7 @@ Version 0.3.0
 To be released.
 
  -  Added `parseLogLevel()` function.
+ -  Added `isLogLevel()` function.
 
 
 Version 0.2.2

logtape/level.test.ts

@@ -0,0 +1,33 @@
+import { assert } from "@std/assert/assert";
+import { assertEquals } from "@std/assert/assert-equals";
+import { assertFalse } from "@std/assert/assert-false";
+import { assertThrows } from "@std/assert/assert-throws";
+import { isLogLevel, parseLogLevel } from "./level.ts";
+
+Deno.test("parseLogLevel()", () => {
+  assertEquals(parseLogLevel("debug"), "debug");
+  assertEquals(parseLogLevel("info"), "info");
+  assertEquals(parseLogLevel("warning"), "warning");
+  assertEquals(parseLogLevel("error"), "error");
+  assertEquals(parseLogLevel("fatal"), "fatal");
+  assertEquals(parseLogLevel("DEBUG"), "debug");
+  assertEquals(parseLogLevel("INFO"), "info");
+  assertEquals(parseLogLevel("WARNING"), "warning");
+  assertEquals(parseLogLevel("ERROR"), "error");
+  assertEquals(parseLogLevel("FATAL"), "fatal");
+  assertThrows(
+    () => parseLogLevel("invalid"),
+    TypeError,
+    "Invalid log level: invalid.",
+  );
+});
+
+Deno.test("isLogLevel()", () => {
+  assert(isLogLevel("debug"));
+  assert(isLogLevel("info"));
+  assert(isLogLevel("warning"));
+  assert(isLogLevel("error"));
+  assert(isLogLevel("fatal"));
+  assertFalse(isLogLevel("DEBUG"));
+  assertFalse(isLogLevel("invalid"));
+});

logtape/level.ts

@@ -23,3 +23,23 @@ export function parseLogLevel(level: string): LogLevel {
       throw new TypeError(`Invalid log level: ${level}.`);
   }
 }
+
+/**
+ * Checks if a string is a valid log level.  This function can be used as
+ * as a type guard to narrow the type of a string to a {@link LogLevel}.
+ *
+ * @param level The log level as a string.  This is case-sensitive.
+ * @returns `true` if the string is a valid log level.
+ */
+export function isLogLevel(level: string): level is LogLevel {
+  switch (level) {
+    case "debug":
+    case "info":
+    case "warning":
+    case "error":
+    case "fatal":
+      return true;
+    default:
+      return false;
+  }
+}

logtape/mod.ts

@@ -19,7 +19,7 @@ export {
   defaultTextFormatter,
   type TextFormatter,
 } from "./formatter.ts";
-export { type LogLevel, parseLogLevel } from "./level.ts";
+export { isLogLevel, type LogLevel, parseLogLevel } from "./level.ts";
 export { getLogger, type Logger } from "./logger.ts";
 export type { LogRecord } from "./record.ts";
 export {