babel.md

Configuring Babel

Translations: Français

AVA uses Babel 7 so you can use the latest JavaScript syntax in your tests. We do this by compiling test and helper files using our @ava/stage-4 preset. We also use a second preset, @ava/transform-test-files to enable enhanced assertion messages and detect improper use of t.throws() assertions.

By default our Babel pipeline is applied to test and helper files ending in .js. If your project uses Babel then we'll automatically compile these files using your project's Babel configuration. The @ava/transform-helper-files preset is applied first, and the @ava/stage-4 last.

If you are using Babel for your source files then you must also configure source compilation.

Customize how AVA compiles your test files

You can override the default Babel configuration AVA uses for test file compilation in package.json or ava.config.js. For example, the configuration below adds support for JSX syntax and stage 3 features:

{
	"ava": {
		"babel": {
			"testOptions": {
				"plugins": ["@babel/plugin-syntax-jsx"],
				"presets": ["@babel/preset-stage-3"]
			}
		}
	}
}

All .babelrc options are allowed inside the testOptions object.

Reset AVA's cache

AVA caches the compiled test and helper files. It automatically recompiles these files when you change them, however it can't detect updates of your Babel plugins and presets, or changes to your Babel configuration files.

Instead run the following to reset AVA's cache when you change the configuration or update plugins or presets:

$ npx ava --reset-cache

Add additional extensions

You can configure AVA to recognize additional file extensions and compile those test & helper files using Babel:

{
	"ava": {
		"babel": {
			"extensions": [
				"js",
				"jsx"
			]
		}
	}
}

See also AVA's extensions option.

Make AVA skip your project's Babel options

You may not want AVA to use your project's Babel options, for example if your project is relying on Babel 6. You can set the babelrc option to false:

{
	"ava": {
		"babel": {
			"testOptions": {
				"babelrc": false
			}
		}
	}
}

Disable AVA's stage-4 preset

You can disable AVA's stage-4 preset:

{
	"ava": {
		"babel": {
			"testOptions": {
				"presets": [
					["module:ava/stage-4", false]
				]
			}
		}
	}
}

Note that this does not stop AVA from compiling your test files using Babel.

You must disable the preset by configuring it in the testOptions. AVA will still apply the preset if you configure it in other files (for instance a .babelrc file). This is due to a Babel issue.

Preserve ES module syntax

By default AVA's stage-4 preset will convert ES module syntax to CommonJS. This can be disabled:

{
	"ava": {
		"babel": {
			"testOptions": {
				"presets": [
					["module:ava/stage-4", {"modules": false}]
				]
			}
		}
	}
}

You must configure the preset in the testOptions in order to preserve the ES module syntax. AVA will still apply the preset if you configure it in other files (for instance a .babelrc file). This is due to a Babel issue.

You'll have to use the esm module so that AVA can still load your test files. See our recipe for details.

Disable AVA's Babel pipeline

You can completely disable AVA's use of Babel:

{
	"ava": {
		"babel": false,
		"compileEnhancements": false
	}
}

Use Babel polyfills

AVA lets you write your tests using new JavaScript syntax, even on Node.js versions that otherwise wouldn't support it. However, it doesn't add or modify built-ins of your current environment. Using AVA would, for example, not provide modern features such as Object.entries() to an underlying Node.js 6 environment.

By loading Babel's polyfill module you can opt in to these features. Note that this will modify the environment, which may influence how your program behaves.

You can enable the polyfill module by adding it to AVA's require option:

{
	"ava": {
		"require": [
			"@babel/polyfill"
		]
	}
}

You'll need to install @babel/polyfill yourself.

Compile sources

AVA does not currently compile source files. You'll have to load Babel's register module, which will compile source files as needed.

You can enable the register module by adding it to AVA's require option:

{
	"ava": {
		"require": [
			"@babel/register"
		]
	}
}

You'll need to install @babel/register yourself.

@babel/register will also process your test and helper files. For most use cases this is unnecessary. If you create a new file that requires @babel/register you can tell it which file paths to ignore. For instance in your test directory create _register.js:

// test/_register.js:
require('@babel/register')({
	// These patterns are relative to the project directory (where the `package.json` file lives):
	ignore: ['node_modules/*', 'test/*']
});

Now instead of requiring @babel/register, require test/_register instead:

{
	"ava": {
		"require": [
			"test/_register.js"
		]
	}
}

Note that loading @babel/register in every worker process has a non-trivial performance cost. If you have lots of test files, you may want to consider using a build step to compile your sources before running your tests. This isn't ideal, since it complicates using AVA's watch mode, so we recommend using @babel/register until the performance penalty becomes too great. Setting up a precompilation step is out of scope for this document, but we recommend you check out one of the many build systems that support Babel. There is an issue discussing ways we could make this experience better.