Documentation Grafana k6 Using k6 JavaScript and TypeScript mode

JavaScript and TypeScript compatibility mode

You can write k6 tests in various ECMAScript versions:

• ES6+ JavaScript with ES modules (ESM).
• ES6+ JavaScript with CommonJS modules.

k6 supports both module types and most ES6+ features in all k6 execution modes: local, distributed, and cloud.

Additionally, k6 also has experimental support for esbuild, to transpile TypeScript (TS) code.

Some users prefer to bundle their test code outside k6. For this reason, k6 offers three JavaScript compatibility modes:

• Extended mode: The default option.
• Experimental enhanced mode: The experimental option, supporting TS.
• Base mode: After v0.53.0 this is almost the same as extended, but doesn’t alias global to globalThis - a nodejs compatibility.

When running tests, you can change the mode by using the --compatibility-mode option:

Extended mode

By default, k6 uses the --compatibility-mode=extended mode:

bash

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$ k6 run script.js

After v0.53.0 the only difference with base is that global (node’s global variable) is aliased to the value of globalThis.

Experimental enhanced mode

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$ k6 run --compatibility-mode=experimental_enhanced script.ts

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$ K6_COMPATIBILITY_MODE=experimental_enhanced k6 run script.ts

The experimental enhanced mode is similar to the extended mode, but it uses esbuild instead of Babel to transpile TypeScript (TS) code.

TypeScript support is partial as it removes the type information but doesn’t provide type safety.

Base mode

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$ k6 run --compatibility-mode=base script.js

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$ K6_COMPATIBILITY_MODE=base k6 run script.js

After v0.53.0 there isn’t a big reason to use this. Before that it was dropping ESM support for usually improved startup speed.

CommonJS Example

JavaScript

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const http = require('k6/http');
const k6 = require('k6');

module.exports.options = {
  vus: 10,
  duration: '30s',
};

module.exports.default = function () {
  http.get('http://test.k6.io');
  k6.sleep(1);
};

⚠️ About require()

Note that require() is a custom k6 implementation of module loading, which doesn’t behave in the same way as the require() call in Node.js. Specifically, it only handles loading of built-in k6 modules, scripts on the local filesystem, and remote scripts over HTTP(S), but it does not support the Node.js module resolution algorithm.

Bundling with Babel outside of k6

The examples below demonstrate the use of Babel with bundlers like Webpack and Rollup:

• k6-template-es6: Template using Webpack and Babel to bundle k6 tests.
• k6-rollup-example: Example using Rollup and Babel to bundle a testing project.

Read more

• Running large tests: Optimize k6 for better performance.
• k6 Modules: Different options to import modules in k6.
• k6 Archive Command: The k6 archive command bundles all k6 test dependencies into a tar file, which can then be used for execution. It may also reduce the execution startup time.