---
title: "JavaScript and TypeScript compatibility mode | Grafana k6 documentation"
description: "k6 supports running test scripts with different compatibility modes using --compatibility-mode"
---

# JavaScript compatibility mode

> Note
> 
> If you’re using k6 v0.53 or higher, the compatibility mode feature doesn’t have much impact on the k6 default behavior. Refer to [this GitHub issue](https://github.com/grafana/k6/issues/3864) for more details.
> 
> Starting on k6 v0.57, TypeScript support is enabled by default, and the `experimental-enhanced-mode` option has been removed.

k6 offers two JavaScript compatibility modes:

- [Base mode](#base-mode): Only uses native support in k6 and the underlying JavaScript runtime. For k6 v0.53.0 or higher, it has the same functionality as `extended` apart from the `global` aliasing.
- [Extended mode](#extended-mode): Similar to base mode, with an additional alias from `global` to `globalThis` for Node.js compatibility. This is the default mode.

After k6 v0.53.0, the only difference between the base and extended modes is that `global`, the Node.js global variable, is aliased to the value of `globalThis`.

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

Expand table

| Env                     | CLI                    | Code / Config file | Default      |
|-------------------------|------------------------|--------------------|--------------|
| `K6_COMPATIBILITY_MODE` | `--compatibility-mode` | N/A                | `"extended"` |

## Extended mode

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

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

```bash
k6 run script.js
```

## Base mode

cli env

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

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

```cli
k6 run --compatibility-mode=base script.js
```

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

```env
K6_COMPATIBILITY_MODE=base k6 run script.js
```

## Typescript support

cli env

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

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

```cli
k6 run script.ts
```

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

```env
k6 run script.ts
```

k6 uses [esbuild](https://esbuild.github.io/) to transpile TypeScript (TS) code for all files that have the `.ts` extension.

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

### CommonJS Example

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

```javascript
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](https://nodejs.org/api/modules.html#modules_require_id). 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](https://nodejs.org/api/modules.html#modules_all_together).

## Bundling with Babel outside of k6

The examples below demonstrate the use of Babel with bundlers like [Webpack](https://webpack.js.org/) and [Rollup](https://rollupjs.org/):

- [k6-template-es6](https://github.com/grafana/k6-template-es6): Template using Webpack and Babel to bundle k6 tests.
- [k6-rollup-example](https://github.com/grafana/k6-rollup-example): Example using Rollup and Babel to bundle a testing project.

## Read more

- [Running large tests](/docs/k6/next/testing-guides/running-large-tests/): Optimize k6 for better performance.
- [k6 Modules](/docs/k6/next/using-k6/modules/): Different options to import modules in k6.
- [k6 Archive Command](/docs/k6/next/reference/archive/): 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.