@joeyparrish/karma-babel-preprocessor
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Preprocessor to compile ES6 on the fly with babel.
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# karma-babel-preprocessor
> Preprocessor to compile ES6 on the fly with [babel](https://github.com/6to5/babel).
This fork of the original adds caching. See `cachePath` below.
**babel and karma-babel-preprocessor only convert ES6 modules to CommonJS/AMD/SystemJS/UMD. If you choose CommonJS, you still need to resolve and concatenate CommonJS modules on your own. We recommend [karma-browserify](https://github.com/Nikku/karma-browserify) + [babelify](https://github.com/babel/babelify) or [webpack](https://github.com/webpack/karma-webpack) + [babel-loader](https://github.com/babel/babel-loader) in such cases.**
## Installation
With babel 7.x:
```bash
npm install karma-babel-preprocessor @babel/core @babel/preset-env --save-dev
```
With babel 6.x:
```bash
npm install karma-babel-preprocessor@7 babel-core babel-preset-env --save-dev
```
As of Babel 6.0, [you need to tell Babel which features to use](http://babeljs.io/docs/plugins/). [@babel/preset-env](http://babeljs.io/docs/plugins/preset-env/) would be the most common one.
## Configuration
See [babel options](https://babeljs.io/docs/usage/options) for more details.
Given `options` properties are passed to babel.
In addition to the `options` property, you can configure any babel options with function properties. This is useful when you want to give different babel options from file to file.
For example, inline sourcemap configuration would look like the following.
```js
module.exports = function (config) {
config.set({
preprocessors: {
'src/**/*.js': ['babel'],
'test/**/*.js': ['babel']
},
babelPreprocessor: {
options: {
presets: ['@babel/preset-env'],
sourceMap: 'inline'
},
filename: function (file) {
return file.originalPath.replace(/\.js$/, '.es5.js');
},
sourceFileName: function (file) {
return file.originalPath;
}
}
});
};
```
### Caching
Adding the field `cachePath` will enable caching. Cached output from babel
will be stored into that file, along with md5 hashes of the original contents
of each file. If an original file hasn't changed, the cached babel-processed
results will be reused.
```js
module.exports = function (config) {
config.set({
preprocessors: {
'src/**/*.js': ['babel'],
'test/**/*.js': ['babel']
},
babelPreprocessor: {
cachePath: '.babel-cache',
options: {
presets: ['@babel/preset-env'],
sourceMap: 'inline'
},
}
});
};
```
### Don't preprocess third-party libraries
Third-party libraries may not work properly if you apply `karma-babel-preprocessor` to them. It also introduces unnecessary overhead. Make sure to explicitly specify files that you want to preprocess.
OK:
```js
module.exports = function (config) {
config.set({
preprocessors: {
'src/**/*.js': ['babel'],
'test/**/*.js': ['babel']
},
// ...
});
};
```
NG:
```js
module.exports = function (config) {
config.set({
preprocessors: {
'./**/*.js': ['babel']
},
// ...
});
};
```
Because it preprocesses files in `node_modules` and may break third-party libraries like jasmine #18.
### Polyfill
If you need [polyfill](https://babeljs.io/docs/usage/polyfill/), make sure to include it in `files`.
```bash
npm install @babel/polyfill --save-dev
```
```js
module.exports = function (config) {
config.set({
files: [
'node_modules/@babel/polyfill/dist/polyfill.js',
// ...
],
// ...
});
});
```
### Karma's plugins option
In most cases, you don't need to explicitly specify `plugins` option. By default, Karma loads all sibling NPM modules which have a name starting with karma-*. If need to do so for some reason, make sure to include `'karma-babel-preprocessor'` in it.
```js
module.exports = function (config) {
config.set({
plugins: [
'karma-jasmine',
'karma-chrome-launcher',
'karma-babel-preprocessor'
],
// ...
});
};
```
## Custom preprocessor
karma-babel-preprocessor supports custom preprocessor. Set `base: 'babel'` in addition to normal preprocessor config.
```js
module.exports = function (config) {
config.set({
preprocessors: {
'src/**/*.js': ['babelSourceMap'],
'test/**/*.js': ['babelSourceMap']
},
customPreprocessors: {
babelSourceMap: {
base: 'babel',
options: {
presets: ['@babel/preset-env'],
sourceMap: 'inline'
},
filename: function (file) {
return file.originalPath.replace(/\.js$/, '.es5.js');
},
sourceFileName: function (file) {
return file.originalPath;
}
},
// Other custom preprocessors...
}
});
};
```