Add last modify field "mtime" for FileBlob (#1431) (#2491)

* Add lastModified field for FileBlob (#1431)

lastModified value is epoch timestamp in millisecond unit.

* update according to review comment.

2 files changed, 19 insertions, 0 deletions

diff --git a/test/js/bun/io/bun-write.test.js b/test/js/bun/io/bun-write.test.js
index c3b9b187b..ab8063f16 100644
--- a/test/js/bun/io/bun-write.test.js
+++ b/test/js/bun/io/bun-write.test.js
@@ -2,6 +2,7 @@ import fs from "fs";
 import { it, expect, describe } from "bun:test";
 import path from "path";
 import { gcTick, withoutAggressiveGC } from "harness";
+import { tmpdir } from "os";
 
 it("Bun.write blob", async () => {
   await Bun.write(Bun.file("/tmp/response-file.test.txt"), Bun.file(path.join(import.meta.dir, "fetch.js.txt")));
@@ -147,6 +148,23 @@ it("Bun.file empty file", async () => {
   await gcTick();
 });
 
+it("Bun.file lastModified update", async () => {
+  const file = Bun.file(tmpdir() + "/bun.test.lastModified.txt");
+  await gcTick();
+  // setup
+  await Bun.write(file, "test text.");
+  const lastModified0 = file.lastModified;
+
+  // sleep some time and write the file again.
+  await Bun.sleep(10);
+  await Bun.write(file, "test text2.");
+  const lastModified1 = file.lastModified;
+
+  // ensure the last modified timestamp is updated.
+  expect(lastModified1).toBeGreaterThan(lastModified0);
+  await gcTick();
+});
+
 it("Bun.file as a Blob", async () => {
   const filePath = path.join(import.meta.path, "../fetch.js.txt");
   const fixture = fs.readFileSync(filePath, "utf8");
diff --git a/test/js/web/fetch/fetch.test.ts b/test/js/web/fetch/fetch.test.ts
index 183c5dc77..cc59ba3f6 100644
--- a/test/js/web/fetch/fetch.test.ts
+++ b/test/js/web/fetch/fetch.test.ts
@@ -540,6 +540,7 @@ describe("Bun.file", () => {
     writeFileSync(path, buffer);
     const file = Bun.file(path);
     expect(blob.size).toBe(file.size);
+    expect(file.lastModified).toBeGreaterThan(0);
     return file;
   });