The Broccoli Plugin Base Class


Example Usage

``js
const Plugin = require('broccoli-plugin');

class MyPlugin extends Plugin {
constructor(inputNodes, options = {}) {
super(inputNodes, {
annotation: options.annotation,
// see options in the below README to see a full list of constructor options
});
}

build() {
// Read files from this.inputPaths, and write files to this.outputPath.
// Silly example:

// Read 'foo.txt' from the third input node
const input = this.input.readFileSync(foo.txt);
const output = someCompiler(input);

// Write to 'bar.txt' in this node's output
this.output.writeFileSync(bar.txt, output);
}
}
`

Reference

$3

Call this base class constructor from your subclass constructor.

- inputNodes: An array of node objects that this plugin will read from.
Nodes are usually other plugin instances; they were formerly known as
"trees".

- options

- name: The name of this plugin class. Defaults to this.constructor.name.
- annotation: A descriptive annotation. Useful for debugging, to tell
multiple instances of the same plugin apart.
- persistentOutput: If true, the output directory is not automatically
emptied between builds.
- needsCache : If true, a cache directory is created automatically
and the path is set at cachePath. If false, a cache directory is not created
and this.cachePath is undefined. Defaults to true.
- volatile : If true, memoization will not be applied and the build method will
always be called regardless if the inputNodes have changed. Defaults to false.
- trackInputChanges : If true, a change object will be passed to the build method which contains
information about which input has changed since the last build. Defaults to false.

$3

Override this method in your subclass. It will be called on each (re-)build.

This function will typically access the following read-only properties:

- this.inputPaths: An array of paths on disk corresponding to each node in
inputNodes. Your plugin will read files from these paths.

- this.outputPath: The path on disk corresponding to this plugin instance
(this node). Your plugin will write files to this path. This directory is
emptied by Broccoli before each build, unless the persistentOutput options
is true.

- this.cachePath: The path on disk to an auxiliary cache directory. Use this
to store files that you want preserved between builds. This directory will
only be deleted when Broccoli exits. If a cache directory is not needed, set
needsCache to false when calling broccoli-plugin constructor.

All paths stay the same between builds.

To perform asynchronous work, return a promise. The promise's eventual value
is ignored (typically null).

To report a compile error, throw it or return a rejected promise. Also see
section "Error Objects" below.

If the trackInputChanges option was set to true, an object will be passed to the
build method with the shape of:

`js
{
changedNodes: [true, true, ...]
}
`

This array contain a booleans corresponding to each input node as to whether or not that node changed since the last rebuild. For the initial build all values in the array will be true.

$3

Advanced usage only.

Return the object on which Broccoli will call obj.build(). Called once after
instantiation. By default, returns this. Plugins do not usually need to
override this, but it can be useful for base classes that other plugins in turn
derive from, such as
broccoli-caching-writer.

For example, to intercept .build() calls, you might
return { build: this.buildWrapper.bind(this) }.
Or, to hand off the plugin implementation to a completely separate object:
return new MyPluginWorker(this.inputPaths, this.outputPath, this.cachePath),
where MyPluginWorker provides a .build method.

$3

To help with displaying clear error messages for build errors, error objects
may have the following optional properties in addition to the standard
message property:

- file: Path of the file in which the error occurred, relative to one of the
inputPaths directories
- treeDir: The path that file is relative to. Must be an element of
this.inputPaths. (The name treeDir is for historical reasons.)
- line: Line in which the error occurred (one-indexed)
- column: Column in which the error occurred (zero-indexed)

$3

An api which enables a plugin to easily read from one or more input directories ergonomically and safely.

_Note: We recommend users stop using this.inputPaths and instead rely on this.input. Our plan at present is to strongly consider deprecation of this.inputPaths once this.input has had time to bake._

this.input's features:

- this.input reads from the provided inputPaths. No path concatenation required.
- this.input provides readOnly file system APIs. This prevents a plugin from erroneously mutating its inputs.
- this.input provides a merged view of inputs, this allows every plugin to easily support multiple inputs, without the use of broccoli-merge-trees or implementing a complex merge algorithm.
- this.input.at(index) provides access to each individual input if desired.

Example:

`js
// old
fs.readFileSync(this.inputPaths[0] + '/file.txt');

// new (merged): Most Common
this.input.readFileSync('file.txt');

// new (indexed): For when you need to disambiguate between inputs.
this.input.at(0).readFileSync('file.txt);

// ReadOnly
this.input.writeFileSync // throws error
`

$3

- readFileSync
- existsSync
- lstatSync
- statSync
- readdirSync
- at

Read more about input here

Note: input will be available only after the build starts.

$3

An api which enables a plugin to easily write to the output directory ergonomically and safely.

_Note: We recommend users stop using this.outputPath and instead rely on this.output. Our plan at present is to strongly consider deprecation of this.outputPath once this.output has had time to bake._

this.output's features:

- this.ouput writes to the outputPath. No path concatenation required.
- this.output provides read operations on the outputPath. No path concatenation required.

Ex:

`js
// old
fs.writeFileSync(this.outputPath + '/file.txt', 'text');

// new
this.output.writeFileSync('file.txt', 'text');
`

$3

- readFileSync
- existsSync
- lstatSync
- readdirSync
- statSync
- writeFileSync
- appendFileSync
- rmdirSync
- mkdirSync

Read more about APIs present in output here.

Note: output will be available only after the build` starts.