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Documentation Grafana k6 JavaScript API k6/experimental fs open

open

The open function opens a file and returns a promise that resolves to a File instance. Unlike the traditional open function, which loads a file multiple times into memory, the filesystem module reduces memory usage by loading the file as little possible, and sharing the same memory space between all VUs. This approach reduces the risk of encountering out-of-memory errors, especially in load tests involving large files.

Asynchronous nature

It’s important to note that open is asynchronous and returns a Promise. Due to k6’s current limitation with the Init context (which doesn’t support asynchronous functions directly), you need to use an asynchronous wrapper like this:

JavaScript

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JavaScript Copy

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

Parameters

Returns

A promise resolving to a File instance.

Example

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import { open } from 'k6/experimental/fs';

// k6 doesn't support async in the init context. We use a top-level async function for `await`.
//
// Each Virtual User gets its own `file` copy.
// So, operations like `seek` or `read` won't impact other VUs.
let file;
(async function () {
  file = await open('bonjour.txt');
})();

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

  console.log(JSON.stringify(fileinfo));
}