3 files changed, 64 insertions, 0 deletions
diff --git a/fs/eol.ts b/fs/eol.ts
new file mode 100644
index 000000000..af5e81ead
--- /dev/null
+++ b/fs/eol.ts
@@ -0,0 +1,31 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
+/** EndOfLine character enum */
+export enum EOL {
+  LF = "\n",
+  CRLF = "\r\n"
+}
+
+const regDetect = /(?:\r?\n)/g;
+
+/**
+ * Detect the EOL character for string input.
+ * returns null if no newline
+ */
+export function detect(content: string): EOL | null {
+  const d = content.match(regDetect);
+  if (!d || d.length === 0) {
+    return null;
+  }
+  const crlf = d.filter(x => x === EOL.CRLF);
+  if (crlf.length > 0) {
+    return EOL.CRLF;
+  } else {
+    return EOL.LF;
+  }
+}
+
+/** Format the file to the targeted EOL */
+export function format(content: string, eol: EOL): string {
+  return content.replace(regDetect, eol);
+}
diff --git a/fs/eol_test.ts b/fs/eol_test.ts
new file mode 100644
index 000000000..eafdb697e
--- /dev/null
+++ b/fs/eol_test.ts
@@ -0,0 +1,32 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+import { test } from "../testing/mod.ts";
+import { assertEquals } from "../testing/asserts.ts";
+import { format, detect, EOL } from "./eol.ts";
+
+const CRLFinput = "deno\r\nis not\r\nnode";
+const Mixedinput = "deno\nis not\r\nnode";
+const Mixedinput2 = "deno\r\nis not\nnode";
+const LFinput = "deno\nis not\nnode";
+const NoNLinput = "deno is not node";
+
+test(function detectCRLF() {
+  assertEquals(detect(CRLFinput), EOL.CRLF);
+});
+test(function detectLF() {
+  assertEquals(detect(LFinput), EOL.LF);
+});
+test(function detectNoNewLine() {
+  assertEquals(detect(NoNLinput), null);
+});
+test(function testFormat() {
+  assertEquals(format(CRLFinput, EOL.LF), LFinput);
+  assertEquals(format(LFinput, EOL.LF), LFinput);
+  assertEquals(format(LFinput, EOL.CRLF), CRLFinput);
+  assertEquals(format(CRLFinput, EOL.CRLF), CRLFinput);
+  assertEquals(format(CRLFinput, EOL.CRLF), CRLFinput);
+  assertEquals(format(NoNLinput, EOL.CRLF), NoNLinput);
+  assertEquals(format(Mixedinput, EOL.CRLF), CRLFinput);
+  assertEquals(format(Mixedinput, EOL.LF), LFinput);
+  assertEquals(format(Mixedinput2, EOL.CRLF), CRLFinput);
+  assertEquals(format(Mixedinput2, EOL.LF), LFinput);
+});
diff --git a/fs/test.ts b/fs/test.ts
index 5cff8e174..dac0d350d 100644
--- a/fs/test.ts
+++ b/fs/test.ts
@@ -3,6 +3,7 @@ import "./path/test.ts";
 import "./walk_test.ts";
 import "./globrex_test.ts";
 import "./glob_test.ts";
+import "./eol_test.ts";
 import "./exists_test.ts";
 import "./empty_dir_test.ts";
 import "./ensure_dir_test.ts";