Writing Files

Many applications need to write files to disk. Deno provides a simple interface for writing files.

The easiest way to write a file, is to dump an entire buffer into the file at once.

const bytes = new Uint8Array([72, 101, 108, 108, 111]);
await Deno.writeFile("hello.txt", bytes, { mode: 0o644 });

You can also write a string instead of a byte array.

await Deno.writeTextFile("hello.txt", "Hello World");

For more granular writes, open a new file for writing.

const file = await Deno.create("hello.txt");

You can write chunks of data to the file.

const written = await file.write(bytes);
console.log(`${written} bytes written.`);

A `file.write` returns the number of bytes written, as it might not write all bytes passed. Use the `writeAll` utility from `std/streams` to make sure the entire buffer is written.

import { writeAll } from "https://deno.land/std@0.192.0/streams/write_all.ts";
await writeAll(file, new TextEncoder().encode("World!"));

Make sure to close the file after you are done with it.

file.close();

Synchronous writing is also supported.

Deno.writeFileSync("hello.txt", bytes);
Deno.writeTextFileSync("hello.txt", "Hello World");
const f = Deno.createSync("hello.txt");
import { writeAllSync } from "https://deno.land/std@0.192.0/streams/write_all.ts";
writeAllSync(f, new TextEncoder().encode("World!"));
f.close();

The `--allow-write` permission is required to write files.

Run this example locally using the Deno CLI:

deno run --allow-read --allow-write https://byexample-y960a7h1v5j0.deno.dev/writing-files.ts

Additional resources:

Reading Files Deleting Files