Utils

Use Bun’s utility functions to work with the runtime

Bun.version

A string containing the version of the bun CLI that is currently running.

terminal

Bun.version;
// => "1.3.3"

Bun.revision

The git commit of Bun that was compiled to create the current bun CLI.

terminal

Bun.revision;
// => "f02561530fda1ee9396f51c8bc99b38716e38296"

Bun.env

An alias for process.env.

Bun.main

An absolute path to the entrypoint of the current program (the file that was executed with bun run).

script.ts

Bun.main;
// /path/to/script.ts

This is particular useful for determining whether a script is being directly executed, as opposed to being imported by another script.

if (import.meta.path === Bun.main) {
  // this script is being directly executed
} else {
  // this file is being imported from another script
}

This is analogous to the require.main = module trick in Node.js.

Bun.sleep()

Bun.sleep(ms: number)

Returns a Promise that resolves after the given number of milliseconds.

console.log("hello");
await Bun.sleep(1000);
console.log("hello one second later!");

Alternatively, pass a Date object to receive a Promise that resolves at that point in time.

const oneSecondInFuture = new Date(Date.now() + 1000);

console.log("hello");
await Bun.sleep(oneSecondInFuture);
console.log("hello one second later!");

Bun.sleepSync()

Bun.sleepSync(ms: number)

A blocking synchronous version of Bun.sleep.

console.log("hello");
Bun.sleepSync(1000); // blocks thread for one second
console.log("hello one second later!");

Bun.which()

Bun.which(bin: string)

Returns the path to an executable, similar to typing which in your terminal.

const ls = Bun.which("ls");
console.log(ls); // "/usr/bin/ls"

By default Bun looks at the current PATH environment variable to determine the path. To configure PATH:

const ls = Bun.which("ls", {
  PATH: "/usr/local/bin:/usr/bin:/bin",
});
console.log(ls); // "/usr/bin/ls"

Pass a cwd option to resolve for executable from within a specific directory.

const ls = Bun.which("ls", {
  cwd: "/tmp",
  PATH: "",
});

console.log(ls); // null

You can think of this as a builtin alternative to the which npm package.

Bun.randomUUIDv7()

Bun.randomUUIDv7() returns a UUID v7, which is monotonic and suitable for sorting and databases.

import { randomUUIDv7 } from "bun";

const id = randomUUIDv7();
// => "0192ce11-26d5-7dc3-9305-1426de888c5a"

A UUID v7 is a 128-bit value that encodes the current timestamp, a random value, and a counter. The timestamp is encoded using the lowest 48 bits, and the random value and counter are encoded using the remaining bits.

The timestamp parameter defaults to the current time in milliseconds. When the timestamp changes, the counter is reset to a pseudo-random integer wrapped to 4096. This counter is atomic and threadsafe, meaning that using Bun.randomUUIDv7() in many Workers within the same process running at the same timestamp will not have colliding counter values.

The final 8 bytes of the UUID are a cryptographically secure random value. It uses the same random number generator used by crypto.randomUUID() (which comes from BoringSSL, which in turn comes from the platform-specific system random number generator usually provided by the underlying hardware).

namespace Bun {
  function randomUUIDv7(encoding?: "hex" | "base64" | "base64url" = "hex", timestamp?: number = Date.now()): string;
  /**
   * If you pass "buffer", you get a 16-byte buffer instead of a string.
   */
  function randomUUIDv7(encoding: "buffer", timestamp?: number = Date.now()): Buffer;

  // If you only pass a timestamp, you get a hex string
  function randomUUIDv7(timestamp?: number = Date.now()): string;
}

You can optionally set encoding to "buffer" to get a 16-byte buffer instead of a string. This can sometimes avoid string conversion overhead.

buffer.ts

const buffer = Bun.randomUUIDv7("buffer");

base64 and base64url encodings are also supported when you want a slightly shorter string.

base64.ts

const base64 = Bun.randomUUIDv7("base64");
const base64url = Bun.randomUUIDv7("base64url");

Bun.peek()

Bun.peek(prom: Promise)

Reads a promise’s result without await or .then, but only if the promise has already fulfilled or rejected.

import { peek } from "bun";

const promise = Promise.resolve("hi");

// no await!
const result = peek(promise);
console.log(result); // "hi"

This is important when attempting to reduce the number of extraneous microticks in performance-sensitive code. It’s an advanced API — review the examples below before using it in production.

import { peek } from "bun";
import { expect, test } from "bun:test";

test("peek", () => {
  const promise = Promise.resolve(true);

  // no await necessary!
  expect(peek(promise)).toBe(true);

  // if we peek again, it returns the same value
  const again = peek(promise);
  expect(again).toBe(true);

  // if we peek a non-promise, it returns the value
  const value = peek(42);
  expect(value).toBe(42);

  // if we peek a pending promise, it returns the promise again
  const pending = new Promise(() => {});
  expect(peek(pending)).toBe(pending);

  // If we peek a rejected promise, it:
  // - returns the error
  // - does not mark the promise as handled
  const rejected = Promise.reject(new Error("Successfully tested promise rejection"));
  expect(peek(rejected).message).toBe("Successfully tested promise rejection");
});

The peek.status function lets you read the status of a promise without resolving it.

import { peek } from "bun";
import { expect, test } from "bun:test";

test("peek.status", () => {
  const promise = Promise.resolve(true);
  expect(peek.status(promise)).toBe("fulfilled");

  const pending = new Promise(() => {});
  expect(peek.status(pending)).toBe("pending");

  const rejected = Promise.reject(new Error("oh nooo"));
  expect(peek.status(rejected)).toBe("rejected");
});

Bun.openInEditor()

Opens a file in your default editor. Bun auto-detects your editor via the $VISUAL or $EDITOR environment variables.

const currentFile = import.meta.url;
Bun.openInEditor(currentFile);

You can override this via the debug.editor setting in your bunfig.toml.

bunfig.toml

[debug]
editor = "code"

Or specify an editor with the editor param. You can also specify a line and column number.

Bun.openInEditor(import.meta.url, {
  editor: "vscode", // or "subl"
  line: 10,
  column: 5,
});

Bun.deepEquals()

Recursively checks if two objects are equivalent. expect().toEqual() in bun:test uses this internally.

const foo = { a: 1, b: 2, c: { d: 3 } };

// true
Bun.deepEquals(foo, { a: 1, b: 2, c: { d: 3 } });

// false
Bun.deepEquals(foo, { a: 1, b: 2, c: { d: 4 } });

Pass a third boolean parameter to enable “strict” mode. expect().toStrictEqual() in the test runner uses this.

const a = { entries: [1, 2] };
const b = { entries: [1, 2], extra: undefined };

Bun.deepEquals(a, b); // => true
Bun.deepEquals(a, b, true); // => false

In strict mode, the following are considered unequal:

// undefined values
Bun.deepEquals({}, { a: undefined }, true); // false

// undefined in arrays
Bun.deepEquals(["asdf"], ["asdf", undefined], true); // false

// sparse arrays
Bun.deepEquals([, 1], [undefined, 1], true); // false

// object literals vs instances w/ same properties
class Foo {
  a = 1;
}
Bun.deepEquals(new Foo(), { a: 1 }, true); // false

Bun.escapeHTML()

Bun.escapeHTML(value: string | object | number | boolean): string

Escapes the following characters from an input string:

• " becomes "
• & becomes &
• ' becomes '
• < becomes <
• > becomes >

This function is optimized for large input. On an M1X, it processes 480 MB/s - 20 GB/s, depending on how much data is being escaped and whether there is non-ascii text. Non-string types will be converted to a string before escaping.

Bun.stringWidth()

~6,756x faster string-width alternative

Get the column count of a string as it would be displayed in a terminal. Supports ANSI escape codes, emoji, and wide characters.

Example usage:

Bun.stringWidth("hello"); // => 5
Bun.stringWidth("\u001b[31mhello\u001b[0m"); // => 5
Bun.stringWidth("\u001b[31mhello\u001b[0m", { countAnsiEscapeCodes: true }); // => 12

This is useful for:

• Aligning text in a terminal
• Quickly checking if a string contains ANSI escape codes
• Measuring the width of a string in a terminal

This API is designed to match the popular “string-width” package, so that existing code can be ported to Bun and vice versa.

In this benchmark, Bun.stringWidth is a ~6,756x faster than the string-width npm package for input larger than about 500 characters. Big thanks to sindresorhus for their work on string-width!

❯ bun string-width.mjs
cpu: 13th Gen Intel(R) Core(TM) i9-13900
runtime: bun 1.0.29 (x64-linux)

benchmark                                          time (avg)             (min … max)       p75       p99      p995
------------------------------------------------------------------------------------- -----------------------------
Bun.stringWidth     500 chars ascii              37.09 ns/iter   (36.77 ns … 41.11 ns)  37.07 ns  38.84 ns  38.99 ns

❯ node string-width.mjs

benchmark                                          time (avg)             (min … max)       p75       p99      p995
------------------------------------------------------------------------------------- -----------------------------
npm/string-width    500 chars ascii             249,710 ns/iter (239,970 ns … 293,180 ns) 250,930 ns  276,700 ns 281,450 ns

To make Bun.stringWidth fast, we’ve implemented it in native code using optimized SIMD instructions, accounting for Latin1, UTF-16, and UTF-8 encodings. It passes string-width’s tests.

View full benchmark

As a reminder, 1 nanosecond (ns) is 1 billionth of a second. Here’s a reference for converting between units:

Unit	1 Millisecond
ns	1,000,000
µs	1,000
ms	1

terminal

❯ bun string-width.mjs
cpu: 13th Gen Intel(R) Core(TM) i9-13900
runtime: bun 1.0.29 (x64-linux)

benchmark                                          time (avg)             (min … max)       p75       p99      p995
------------------------------------------------------------------------------------- -----------------------------
Bun.stringWidth      5 chars ascii              16.45 ns/iter   (16.27 ns … 19.71 ns)  16.48 ns  16.93 ns  17.21 ns
Bun.stringWidth     50 chars ascii              19.42 ns/iter   (18.61 ns … 27.85 ns)  19.35 ns   21.7 ns  22.31 ns
Bun.stringWidth    500 chars ascii              37.09 ns/iter   (36.77 ns … 41.11 ns)  37.07 ns  38.84 ns  38.99 ns
Bun.stringWidth  5,000 chars ascii              216.9 ns/iter  (215.8 ns … 228.54 ns) 216.23 ns 228.52 ns 228.53 ns
Bun.stringWidth 25,000 chars ascii               1.01 µs/iter     (1.01 µs … 1.01 µs)   1.01 µs   1.01 µs   1.01 µs
Bun.stringWidth      7 chars ascii+emoji         54.2 ns/iter   (53.36 ns … 58.19 ns)  54.23 ns  57.55 ns  57.94 ns
Bun.stringWidth     70 chars ascii+emoji       354.26 ns/iter (350.51 ns … 363.96 ns) 355.93 ns 363.11 ns 363.96 ns
Bun.stringWidth    700 chars ascii+emoji          3.3 µs/iter      (3.27 µs … 3.4 µs)    3.3 µs    3.4 µs    3.4 µs
Bun.stringWidth  7,000 chars ascii+emoji        32.69 µs/iter   (32.22 µs … 45.27 µs)   32.7 µs  34.57 µs  34.68 µs
Bun.stringWidth 35,000 chars ascii+emoji       163.35 µs/iter (161.17 µs … 170.79 µs) 163.82 µs 169.66 µs 169.93 µs
Bun.stringWidth      8 chars ansi+emoji         66.15 ns/iter   (65.17 ns … 69.97 ns)  66.12 ns   69.8 ns  69.87 ns
Bun.stringWidth     80 chars ansi+emoji        492.95 ns/iter  (488.05 ns … 499.5 ns)  494.8 ns 498.58 ns  499.5 ns
Bun.stringWidth    800 chars ansi+emoji          4.73 µs/iter     (4.71 µs … 4.88 µs)   4.72 µs   4.88 µs   4.88 µs
Bun.stringWidth  8,000 chars ansi+emoji         47.02 µs/iter   (46.37 µs … 67.44 µs)  46.96 µs  49.57 µs  49.63 µs
Bun.stringWidth 40,000 chars ansi+emoji        234.45 µs/iter (231.78 µs … 240.98 µs) 234.92 µs 236.34 µs 236.62 µs
Bun.stringWidth     19 chars ansi+emoji+ascii  135.46 ns/iter (133.67 ns … 143.26 ns) 135.32 ns 142.55 ns 142.77 ns
Bun.stringWidth    190 chars ansi+emoji+ascii    1.17 µs/iter     (1.16 µs … 1.17 µs)   1.17 µs   1.17 µs   1.17 µs
Bun.stringWidth  1,900 chars ansi+emoji+ascii   11.45 µs/iter   (11.26 µs … 20.41 µs)  11.45 µs  12.08 µs  12.11 µs
Bun.stringWidth 19,000 chars ansi+emoji+ascii  114.06 µs/iter (112.86 µs … 120.06 µs) 114.25 µs 115.86 µs 116.15 µs
Bun.stringWidth 95,000 chars ansi+emoji+ascii  572.69 µs/iter (565.52 µs … 607.22 µs) 572.45 µs 604.86 µs 605.21 µs

terminal

❯ node string-width.mjs
cpu: 13th Gen Intel(R) Core(TM) i9-13900
runtime: node v21.4.0 (x64-linux)

benchmark                                           time (avg)             (min … max)       p75       p99      p995
-------------------------------------------------------------------------------------- -----------------------------
npm/string-width      5 chars ascii               3.19 µs/iter     (3.13 µs … 3.48 µs)   3.25 µs   3.48 µs   3.48 µs
npm/string-width     50 chars ascii              20.09 µs/iter  (18.93 µs … 435.06 µs)  19.49 µs  21.89 µs  22.59 µs
npm/string-width    500 chars ascii             249.71 µs/iter (239.97 µs … 293.18 µs) 250.93 µs  276.7 µs 281.45 µs
npm/string-width  5,000 chars ascii               6.69 ms/iter     (6.58 ms … 6.76 ms)   6.72 ms   6.76 ms   6.76 ms
npm/string-width 25,000 chars ascii             139.57 ms/iter (137.17 ms … 143.28 ms) 140.49 ms 143.28 ms 143.28 ms
npm/string-width      7 chars ascii+emoji          3.7 µs/iter     (3.62 µs … 3.94 µs)   3.73 µs   3.94 µs   3.94 µs
npm/string-width     70 chars ascii+emoji        23.93 µs/iter   (22.44 µs … 331.2 µs)  23.15 µs  25.98 µs   30.2 µs
npm/string-width    700 chars ascii+emoji       251.65 µs/iter (237.78 µs … 444.69 µs) 252.92 µs 325.89 µs 354.08 µs
npm/string-width  7,000 chars ascii+emoji         4.95 ms/iter     (4.82 ms … 5.19 ms)      5 ms   5.04 ms   5.19 ms
npm/string-width 35,000 chars ascii+emoji        96.93 ms/iter  (94.39 ms … 102.58 ms)  97.68 ms 102.58 ms 102.58 ms
npm/string-width      8 chars ansi+emoji          3.92 µs/iter     (3.45 µs … 4.57 µs)   4.09 µs   4.57 µs   4.57 µs
npm/string-width     80 chars ansi+emoji         24.46 µs/iter     (22.87 µs … 4.2 ms)  23.54 µs  25.89 µs  27.41 µs
npm/string-width    800 chars ansi+emoji        259.62 µs/iter (246.76 µs … 480.12 µs) 258.65 µs 349.84 µs 372.55 µs
npm/string-width  8,000 chars ansi+emoji          5.46 ms/iter     (5.41 ms … 5.57 ms)   5.48 ms   5.55 ms   5.57 ms
npm/string-width 40,000 chars ansi+emoji        108.91 ms/iter  (107.55 ms … 109.5 ms) 109.25 ms  109.5 ms  109.5 ms
npm/string-width     19 chars ansi+emoji+ascii    6.53 µs/iter     (6.35 µs … 6.75 µs)   6.54 µs   6.75 µs   6.75 µs
npm/string-width    190 chars ansi+emoji+ascii   55.52 µs/iter  (52.59 µs … 352.73 µs)  54.19 µs  80.77 µs 167.21 µs
npm/string-width  1,900 chars ansi+emoji+ascii  701.71 µs/iter (653.94 µs … 893.78 µs)  715.3 µs 855.37 µs  872.9 µs
npm/string-width 19,000 chars ansi+emoji+ascii   27.19 ms/iter   (26.89 ms … 27.41 ms)  27.28 ms  27.41 ms  27.41 ms
npm/string-width 95,000 chars ansi+emoji+ascii     3.68 s/iter        (3.66 s … 3.7 s)    3.69 s     3.7 s     3.7 s

TypeScript definition:

namespace Bun {
  export function stringWidth(
    /**
     * The string to measure
     */
    input: string,
    options?: {
      /**
       * If `true`, count ANSI escape codes as part of the string width. If `false`, ANSI escape codes are ignored when calculating the string width.
       *
       * @default false
       */
      countAnsiEscapeCodes?: boolean;
      /**
       * When it's ambiugous and `true`, count emoji as 1 characters wide. If `false`, emoji are counted as 2 character wide.
       *
       * @default true
       */
      ambiguousIsNarrow?: boolean;
    },
  ): number;
}

---

Bun.fileURLToPath()

Converts a file:// URL to an absolute path.

const path = Bun.fileURLToPath(new URL("file:///foo/bar.txt"));
console.log(path); // "/foo/bar.txt"

---

Bun.pathToFileURL()

Converts an absolute path to a file:// URL.

const url = Bun.pathToFileURL("/foo/bar.txt");
console.log(url); // "file:///foo/bar.txt"

---

Bun.gzipSync()

Compresses a Uint8Array using zlib’s GZIP algorithm.

const buf = Buffer.from("hello".repeat(100)); // Buffer extends Uint8Array
const compressed = Bun.gzipSync(buf);

buf; // => Uint8Array(500)
compressed; // => Uint8Array(30)

Optionally, pass a parameters object as the second argument:

zlib compression options

export type ZlibCompressionOptions = {
  /**
   * The compression level to use. Must be between `-1` and `9`.
   * - A value of `-1` uses the default compression level (Currently `6`)
   * - A value of `0` gives no compression
   * - A value of `1` gives least compression, fastest speed
   * - A value of `9` gives best compression, slowest speed
   */
  level?: -1 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9;
  /**
   * How much memory should be allocated for the internal compression state.
   *
   * A value of `1` uses minimum memory but is slow and reduces compression ratio.
   *
   * A value of `9` uses maximum memory for optimal speed. The default is `8`.
   */
  memLevel?: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9;
  /**
   * The base 2 logarithm of the window size (the size of the history buffer).
   *
   * Larger values of this parameter result in better compression at the expense of memory usage.
   *
   * The following value ranges are supported:
   * - `9..15`: The output will have a zlib header and footer (Deflate)
   * - `-9..-15`: The output will **not** have a zlib header or footer (Raw Deflate)
   * - `25..31` (16+`9..15`): The output will have a gzip header and footer (gzip)
   *
   * The gzip header will have no file name, no extra data, no comment, no modification time (set to zero) and no header CRC.
   */
  windowBits?:
    | -9
    | -10
    | -11
    | -12
    | -13
    | -14
    | -15
    | 9
    | 10
    | 11
    | 12
    | 13
    | 14
    | 15
    | 25
    | 26
    | 27
    | 28
    | 29
    | 30
    | 31;
  /**
   * Tunes the compression algorithm.
   *
   * - `Z_DEFAULT_STRATEGY`: For normal data **(Default)**
   * - `Z_FILTERED`: For data produced by a filter or predictor
   * - `Z_HUFFMAN_ONLY`: Force Huffman encoding only (no string match)
   * - `Z_RLE`: Limit match distances to one (run-length encoding)
   * - `Z_FIXED` prevents the use of dynamic Huffman codes
   *
   * `Z_RLE` is designed to be almost as fast as `Z_HUFFMAN_ONLY`, but give better compression for PNG image data.
   *
   * `Z_FILTERED` forces more Huffman coding and less string matching, it is
   * somewhat intermediate between `Z_DEFAULT_STRATEGY` and `Z_HUFFMAN_ONLY`.
   * Filtered data consists mostly of small values with a somewhat random distribution.
   */
  strategy?: number;
};

---

Bun.gunzipSync()

Decompresses a Uint8Array using zlib’s GUNZIP algorithm.

const buf = Buffer.from("hello".repeat(100)); // Buffer extends Uint8Array
const compressed = Bun.gzipSync(buf);

const dec = new TextDecoder();
const uncompressed = Bun.gunzipSync(compressed);
dec.decode(uncompressed);
// => "hellohellohello..."

---

Bun.deflateSync()

Compresses a Uint8Array using zlib’s DEFLATE algorithm.

const buf = Buffer.from("hello".repeat(100));
const compressed = Bun.deflateSync(buf);

buf; // => Buffer(500)
compressed; // => Uint8Array(12)

The second argument supports the same set of configuration options as Bun.gzipSync.

---

Bun.inflateSync()

Decompresses a Uint8Array using zlib’s INFLATE algorithm.

const buf = Buffer.from("hello".repeat(100));
const compressed = Bun.deflateSync(buf);

const dec = new TextDecoder();
const decompressed = Bun.inflateSync(compressed);
dec.decode(decompressed);
// => "hellohellohello..."

---

Bun.zstdCompress() / Bun.zstdCompressSync()

Compresses a Uint8Array using the Zstandard algorithm.

const buf = Buffer.from("hello".repeat(100));

// Synchronous
const compressedSync = Bun.zstdCompressSync(buf);
// Asynchronous
const compressedAsync = await Bun.zstdCompress(buf);

// With compression level (1-22, default: 3)
const compressedLevel = Bun.zstdCompressSync(buf, { level: 6 });

Bun.zstdDecompress() / Bun.zstdDecompressSync()

Decompresses a Uint8Array using the Zstandard algorithm.

const buf = Buffer.from("hello".repeat(100));
const compressed = Bun.zstdCompressSync(buf);

// Synchronous
const decompressedSync = Bun.zstdDecompressSync(compressed);
// Asynchronous
const decompressedAsync = await Bun.zstdDecompress(compressed);

const dec = new TextDecoder();
dec.decode(decompressedSync);
// => "hellohellohello..."

---

Bun.inspect()

Serializes an object to a string exactly as it would be printed by console.log.

const obj = { foo: "bar" };
const str = Bun.inspect(obj);
// => '{\nfoo: "bar" \n}'

const arr = new Uint8Array([1, 2, 3]);
const str = Bun.inspect(arr);
// => "Uint8Array(3) [ 1, 2, 3 ]"

Bun.inspect.custom

This is the symbol that Bun uses to implement Bun.inspect. You can override this to customize how your objects are printed. It is identical to util.inspect.custom in Node.js.

class Foo {
  [Bun.inspect.custom]() {
    return "foo";
  }
}

const foo = new Foo();
console.log(foo); // => "foo"

Bun.inspect.table(tabularData, properties, options)

Format tabular data into a string. Like console.table, except it returns a string rather than printing to the console.

console.log(
  Bun.inspect.table([
    { a: 1, b: 2, c: 3 },
    { a: 4, b: 5, c: 6 },
    { a: 7, b: 8, c: 9 },
  ]),
);
//
// ┌───┬───┬───┬───┐
// │   │ a │ b │ c │
// ├───┼───┼───┼───┤
// │ 0 │ 1 │ 2 │ 3 │
// │ 1 │ 4 │ 5 │ 6 │
// │ 2 │ 7 │ 8 │ 9 │
// └───┴───┴───┴───┘

Additionally, you can pass an array of property names to display only a subset of properties.

console.log(
  Bun.inspect.table(
    [
      { a: 1, b: 2, c: 3 },
      { a: 4, b: 5, c: 6 },
    ],
    ["a", "c"],
  ),
);
//
// ┌───┬───┬───┐
// │   │ a │ c │
// ├───┼───┼───┤
// │ 0 │ 1 │ 3 │
// │ 1 │ 4 │ 6 │
// └───┴───┴───┘

You can also conditionally enable ANSI colors by passing { colors: true }.

console.log(
  Bun.inspect.table(
    [
      { a: 1, b: 2, c: 3 },
      { a: 4, b: 5, c: 6 },
    ],
    {
      colors: true,
    },
  ),
);

---

Bun.nanoseconds()

Returns the number of nanoseconds since the current bun process started, as a number. Useful for high-precision timing and benchmarking.

Bun.nanoseconds();
// => 7288958

---

Bun.readableStreamTo*()

Bun implements a set of convenience functions for asynchronously consuming the body of a ReadableStream and converting it to various binary formats.

const stream = (await fetch("https://bun.com")).body;
stream; // => ReadableStream

await Bun.readableStreamToArrayBuffer(stream);
// => ArrayBuffer

await Bun.readableStreamToBytes(stream);
// => Uint8Array

await Bun.readableStreamToBlob(stream);
// => Blob

await Bun.readableStreamToJSON(stream);
// => object

await Bun.readableStreamToText(stream);
// => string

// returns all chunks as an array
await Bun.readableStreamToArray(stream);
// => unknown[]

// returns all chunks as a FormData object (encoded as x-www-form-urlencoded)
await Bun.readableStreamToFormData(stream);

// returns all chunks as a FormData object (encoded as multipart/form-data)
await Bun.readableStreamToFormData(stream, multipartFormBoundary);

---

Bun.resolveSync()

Resolves a file path or module specifier using Bun’s internal module resolution algorithm. The first argument is the path to resolve, and the second argument is the “root”. If no match is found, an Error is thrown.

Bun.resolveSync("./foo.ts", "/path/to/project");
// => "/path/to/project/foo.ts"

Bun.resolveSync("zod", "/path/to/project");
// => "/path/to/project/node_modules/zod/index.ts"

To resolve relative to the current working directory, pass process.cwd() or "." as the root.

Bun.resolveSync("./foo.ts", process.cwd());
Bun.resolveSync("./foo.ts", "/path/to/project");

To resolve relative to the directory containing the current file, pass import.meta.dir.

Bun.resolveSync("./foo.ts", import.meta.dir);

---

Bun.stripANSI()

~6-57x faster strip-ansi alternative

Bun.stripANSI(text: string): string

Strip ANSI escape codes from a string. This is useful for removing colors and formatting from terminal output.

const coloredText = "\u001b[31mHello\u001b[0m \u001b[32mWorld\u001b[0m";
const plainText = Bun.stripANSI(coloredText);
console.log(plainText); // => "Hello World"

// Works with various ANSI codes
const formatted = "\u001b[1m\u001b[4mBold and underlined\u001b[0m";
console.log(Bun.stripANSI(formatted)); // => "Bold and underlined"

Bun.stripANSI is significantly faster than the popular strip-ansi npm package:

terminal

bun bench/snippets/strip-ansi.mjs

cpu: Apple M3 Max
runtime: bun 1.2.21 (arm64-darwin)

benchmark                               avg (min … max) p75 / p99
------------------------------------------------------- ----------
Bun.stripANSI      11 chars no-ansi        8.13 ns/iter   8.27 ns
                                   (7.45 ns … 33.59 ns)  10.29 ns

Bun.stripANSI      13 chars ansi          51.68 ns/iter  52.51 ns
                                 (46.16 ns … 113.71 ns)  57.71 ns

Bun.stripANSI  16,384 chars long-no-ansi 298.39 ns/iter 305.44 ns
                                (281.50 ns … 331.65 ns) 320.70 ns

Bun.stripANSI 212,992 chars long-ansi    227.65 µs/iter 234.50 µs
                                (216.46 µs … 401.92 µs) 262.25 µs

terminal

node bench/snippets/strip-ansi.mjs

cpu: Apple M3 Max
runtime: node 24.6.0 (arm64-darwin)

benchmark                                avg (min … max) p75 / p99
-------------------------------------------------------- ---------
npm/strip-ansi      11 chars no-ansi      466.79 ns/iter 468.67 ns
                                 (454.08 ns … 570.67 ns) 543.67 ns

npm/strip-ansi      13 chars ansi         546.77 ns/iter 550.23 ns
                                 (532.74 ns … 651.08 ns) 590.35 ns

npm/strip-ansi  16,384 chars long-no-ansi   4.85 µs/iter   4.89 µs
                                     (4.71 µs … 5.00 µs)   4.98 µs

npm/strip-ansi 212,992 chars long-ansi      1.36 ms/iter   1.38 ms
                                     (1.27 ms … 1.73 ms)   1.49 ms

---

Bun.wrapAnsi()

Drop-in replacement for wrap-ansi npm package

Bun.wrapAnsi(input: string, columns: number, options?: WrapAnsiOptions): string

Wrap text to a specified column width while preserving ANSI escape codes, hyperlinks, and handling Unicode/emoji width correctly. This is a native, high-performance alternative to the popular wrap-ansi npm package.

// Basic wrapping at 20 columns
Bun.wrapAnsi("The quick brown fox jumps over the lazy dog", 20);
// => "The quick brown fox\njumps over the lazy\ndog"

// Preserves ANSI escape codes
Bun.wrapAnsi("\u001b[31mThe quick brown fox jumps over the lazy dog\u001b[0m", 20);
// => "\u001b[31mThe quick brown fox\njumps over the lazy\ndog\u001b[0m"

Options

Bun.wrapAnsi("Hello World", 5, {
  hard: true, // Break words that exceed column width (default: false)
  wordWrap: true, // Wrap at word boundaries (default: true)
  trim: true, // Trim leading/trailing whitespace per line (default: true)
  ambiguousIsNarrow: true, // Treat ambiguous-width characters as narrow (default: true)
});

Option	Default	Description
hard	false	If true, break words in the middle if they exceed the column width.
wordWrap	true	If true, wrap at word boundaries. If false, only break at explicit newlines.
trim	true	If true, trim leading and trailing whitespace from each line.
ambiguousIsNarrow	true	If true, treat ambiguous-width Unicode characters as 1 column wide. If false, treat them as 2 columns wide.

TypeScript definition:

namespace Bun {
  export function wrapAnsi(
    /**
     * The string to wrap
     */
    input: string,
    /**
     * The maximum column width
     */
    columns: number,
    /**
     * Wrapping options
     */
    options?: {
      /**
       * If `true`, break words in the middle if they don't fit on a line.
       * If `false`, only break at word boundaries.
       *
       * @default false
       */
      hard?: boolean;
      /**
       * If `true`, wrap at word boundaries when possible.
       * If `false`, don't perform word wrapping (only wrap at explicit newlines).
       *
       * @default true
       */
      wordWrap?: boolean;
      /**
       * If `true`, trim leading and trailing whitespace from each line.
       * If `false`, preserve whitespace.
       *
       * @default true
       */
      trim?: boolean;
      /**
       * When it's ambiguous and `true`, count ambiguous width characters as 1 character wide.
       * If `false`, count them as 2 characters wide.
       *
       * @default true
       */
      ambiguousIsNarrow?: boolean;
    },
  ): string;
}

---

serialize & deserialize in bun:jsc

To save a JavaScript value into an ArrayBuffer & back, use serialize and deserialize from the "bun:jsc" module.

import { serialize, deserialize } from "bun:jsc";

const buf = serialize({ foo: "bar" });
const obj = deserialize(buf);
console.log(obj); // => { foo: "bar" }

Internally, structuredClone and postMessage serialize and deserialize the same way. This exposes the underlying HTML Structured Clone Algorithm to JavaScript as an ArrayBuffer.

---

estimateShallowMemoryUsageOf in bun:jsc

The estimateShallowMemoryUsageOf function returns a best-effort estimate of the memory usage of an object in bytes, excluding the memory usage of properties or other objects it references. For accurate per-object memory usage, use Bun.generateHeapSnapshot.

import { estimateShallowMemoryUsageOf } from "bun:jsc";

const obj = { foo: "bar" };
const usage = estimateShallowMemoryUsageOf(obj);
console.log(usage); // => 16

const buffer = Buffer.alloc(1024 * 1024);
estimateShallowMemoryUsageOf(buffer);
// => 1048624

const req = new Request("https://bun.com");
estimateShallowMemoryUsageOf(req);
// => 167

const array = Array(1024).fill({ a: 1 });
// Arrays are usually not stored contiguously in memory, so this will not return a useful value (which isn't a bug).
estimateShallowMemoryUsageOf(array);
// => 16