---
title: "read | Grafana k6 documentation"
description: "the read method is used to read a chunk of the file."
---

> For a curated documentation index, see [llms.txt](/llms.txt). For the complete documentation index, see [llms-full.txt](/llms-full.txt).

# read

The `read` method is used to read a chunk of the file into an [Uint8Array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) buffer.

It resolves to either the number of bytes read during the operation, or `null` if there was nothing more to read.

## Parameters

Expand table

| Parameter | Type                                                                                                      | Description                       |
|-----------|-----------------------------------------------------------------------------------------------------------|-----------------------------------|
| buffer    | [Uint8Array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) | The buffer to read the data into. |

## Returns

A [Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) resolving to the number of bytes read or `null` if the end of the file has been reached.

## Example

### Reading a file

In the following example, we open a file and read it in chunks of 128 bytes until we reach the end of the file.

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
import { open, SeekMode } from 'k6/experimental/fs';

const file = await open('bonjour.txt');

export default async function () {
  // Seek to the beginning of the file
  await file.seek(0, SeekMode.Start);

  const buffer = new Uint8Array(128);

  let totalBytesRead = 0;
  while (true) {
    // Read into the buffer
    const bytesRead = await file.read(buffer);
    if (bytesRead == null) {
      // EOF
      break;
    }

    // Do something useful with the content of the buffer
    totalBytesRead += bytesRead;

    // If bytesRead is less than the buffer size, we've read the whole file
    if (bytesRead < buffer.byteLength) {
      break;
    }
  }
}
```

### `readAll` helper function

The following helper function can be used to read the entire contents of a file into a [Uint8Array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array) buffer.

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
import { open, SeekMode } from 'k6/experimental/fs';

let file;
(async function () {
  file = await open('bonjour.txt');
})();

async function readAll(file) {
  // Seek to the beginning of the file
  await file.seek(0, SeekMode.Start);

  const fileInfo = await file.stat();
  const buffer = new Uint8Array(fileInfo.size);

  const bytesRead = await file.read(buffer);
  if (bytesRead !== fileInfo.size) {
    throw new Error(
      'unexpected number of bytes read; expected ' +
        fileInfo.size +
        ' but got ' +
        bytesRead +
        ' bytes'
    );
  }

  return buffer;
}

export default async function () {
  // Read the whole file
  const fileContent = await readAll(file);
  console.log(JSON.stringify(fileContent));
}
```