Gracefully handle non-string inputs

index.d.ts

@@ -1,3 +1,5 @@
+type IsString<T> = T extends string ? T : never;
+
 declare const detectNewline: {
 	/**
 	Detect the dominant newline character of a string.
@@ -19,7 +21,8 @@ declare const detectNewline: {
 
 	@returns Returns detected newline or `\n` when no newline character is found.
 	*/
-	graceful(string: string): '\r\n' | '\n';
+	graceful<T>(string: T & IsString<T>): '\r\n' | '\n';
+	graceful(string?: any): '\n';
 };
 
 export = detectNewline;

index.js

@@ -18,4 +18,4 @@ const detectNewline = string => {
 };
 
 module.exports = detectNewline;
-module.exports.graceful = string => detectNewline(string) || '\n';
+module.exports.graceful = string => (typeof string === 'string' && detectNewline(string)) || '\n';

index.test-d.ts

@@ -3,3 +3,8 @@ import detectNewline = require('.');
 
 expectType<'\r\n' | '\n' | undefined>(detectNewline('foo\nbar\nbaz\r\n'));
 expectType<'\r\n' | '\n'>(detectNewline.graceful('foo\nbar\nbaz\r\n'));
+expectType<'\n'>(detectNewline.graceful(null));
+expectType<'\n'>(detectNewline.graceful(undefined));
+expectType<'\n'>(detectNewline.graceful());
+expectType<'\n'>(detectNewline.graceful(1));
+expectType<'\n'>(detectNewline.graceful(['foo', 'bar']));

readme.md

@@ -26,7 +26,7 @@ detectNewline('foo\nbar\nbaz\r\n');
 
 Returns the detected newline or `undefined` when no newline character is found.
 
-### detectNewline.graceful(string)
+### detectNewline.graceful(any)
 
 Returns the detected newline or `\n` when no newline character is found.
 

test.js

@@ -7,5 +7,15 @@ test('main', t => {
 	t.is(detectNewline('foo\nbar\nbaz\r\n'), '\n');
 	t.is(detectNewline('foo\nbar\r\n'), '\n');
 	t.is(detectNewline('foo'), undefined);
+});
+
+test('graceful', t => {
 	t.is(detectNewline.graceful('foo'), '\n');
+	t.is(detectNewline.graceful('foo\r\nbar\r\nbaz\n'), '\r\n');
+	t.is(detectNewline.graceful(null), '\n');
+	t.is(detectNewline.graceful(undefined), '\n');
+	t.is(detectNewline.graceful(), '\n');
+	t.is(detectNewline.graceful(0), '\n');
+	t.is(detectNewline.graceful(true), '\n');
+	t.is(detectNewline.graceful(['foo', 'bar']), '\n');
 });