The Broccoli Plugin Base Class

Example Usage

var Plugin = require('broccoli-plugin');
var path = require('path');

// Create a subclass MyPlugin derived from Plugin
MyPlugin.prototype = Object.create(Plugin.prototype);
MyPlugin.prototype.constructor = MyPlugin;
function MyPlugin(inputNodes, options) {
  options = options || {};
  Plugin.call(this, inputNodes, {
    annotation: options.annotation
  });
  this.options = options;
}

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

  // Read 'foo.txt' from the third input node
  var inputBuffer = fs.readFileSync(path.join(this.inputPaths[2], 'foo.txt'));
  var outputBuffer = someCompiler(inputBuffer);
  // Write to 'bar.txt' in this node's output
  fs.writeFileSync(path.join(this.outputPath, 'bar.txt'), outputBuffer);
};

Reference

new Plugin(inputNodes, options)

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.

Plugin.prototype.build()

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.

Plugin.prototype.getCallbackObject()

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.

Error Objects

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)