Fix the parameters of WriteStream constructor. (#3402)

* Fix the parameters of the `WriteStream` constructor.
Close: https://github.com/oven-sh/bun/issues/3395

* test append mode in `createWriteStream`

* fix lint

* wait first stream finished

2 files changed, 40 insertions, 2 deletions

diff --git a/src/js/node/fs.js b/src/js/node/fs.js
index 2bd752d19..8d9f0d235 100644
--- a/src/js/node/fs.js
+++ b/src/js/node/fs.js
@@ -642,8 +642,8 @@ WriteStream = (function (InternalWriteStream) {
   });
 
   return Object.defineProperty(
-    function WriteStream(options) {
-      return new InternalWriteStream(options);
+    function WriteStream(path, options) {
+      return new InternalWriteStream(path, options);
     },
     Symbol.hasInstance,
     {
diff --git a/test/js/node/fs/fs.test.ts b/test/js/node/fs/fs.test.ts
index 37c3253a4..0353968fe 100644
--- a/test/js/node/fs/fs.test.ts
+++ b/test/js/node/fs/fs.test.ts
@@ -1068,6 +1068,44 @@ describe("createWriteStream", () => {
       expect(exception.code).toBe("ERR_INVALID_ARG_TYPE");
     }
   });
+
+  it("writing in append mode should not truncate the file", async () => {
+    const path = `${tmpdir()}/fs.test.js/${Date.now()}.createWriteStreamAppend.txt`;
+    const stream = createWriteStream(path, {
+      // @ts-ignore-next-line
+      flags: "a",
+    });
+    stream.write("first line\n");
+    stream.end();
+
+    await new Promise((resolve, reject) => {
+      stream.on("error", e => {
+        reject(e);
+      });
+
+      stream.on("finish", () => {
+        resolve(true);
+      });
+    });
+
+    const stream2 = createWriteStream(path, {
+      // @ts-ignore-next-line
+      flags: "a",
+    });
+    stream2.write("second line\n");
+    stream2.end();
+
+    return await new Promise((resolve, reject) => {
+      stream2.on("error", e => {
+        reject(e);
+      });
+
+      stream2.on("finish", () => {
+        expect(readFileSync(path, "utf8")).toBe("first line\nsecond line\n");
+        resolve(true);
+      });
+    });
+  });
 });
 
 describe("fs/promises", () => {