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File

The File class represents a file with methods for reading, seeking, and obtaining file stats. It’s returned by the open function.

Properties

PropertyTypeDescription
pathstringThe absolute path to the file.

Methods

MethodDescription
readReads up to buffer.byteLength bytes from the file into the passed buffer. Returns a promise resolving to the number of bytes read.
seekSets the file position indicator for the file to the passed offset bytes. Returns a promise resolving to the new offset.
statReturns a promise resolving to a FileInfo object with information about the file.

Example

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);

  // About information about the file
  const fileinfo = await file.stat();
  if (fileinfo.name != 'bonjour.txt') {
    throw new Error('Unexpected file name');
  }

  const buffer = new Uint8Array(4);

  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;
    }
  }

  // Check that we read the expected number of bytes
  if (totalBytesRead != fileinfo.size) {
    throw new Error('Unexpected number of bytes read');
  }
}