gulpプラグインを書くにはどうすればいいですか?

1、基礎備蓄

2、基本構造

// 1、 
var through = require('through2');
var gutil = require('gulp-util');
var PluginError = gutil.PluginError;
const PLUGIN_NAME = 'gulp-prefixer';

function prefixStream(prefixText) {
  var stream = through();
  stream.write(prefixText);
  return stream;
}

// 2、  ( )
function gulpPrefixer(prefixText) {
  if (!prefixText) {
    throw new PluginError(PLUGIN_NAME, 'Missing prefix text!');
  }
  prefixText = new Buffer(prefixText); //  prefixText 

  //   stream  
  var stream = through.obj(function(file, enc, cb) {
    if (file.isBuffer()) {
      this.emit('error', new PluginError(PLUGIN_NAME, 'Buffers not supported!'));
      return cb();
    }
    if (file.isStream()) {
      //   streamer
      var streamer = prefixStream(prefixText);
      //   streamer  ，  gulp 
      streamer.on('error', this.emit.bind(this, 'error'));
      //  
      file.contents = file.contents.pipe(streamer);
    }

    //  
    this.push(file);
    //   stream  
    cb();
  });

  //   stream
  return stream;
}

// 3、 （export） 
module.exports = gulpPrefixer;

3、主関数の作成

file.isStream()

4、プラグインの例

var through = require('through2');
var gutil = require('gulp-util');
var applySourceMap = require('vinyl-sourcemaps-apply');
var path = require('path');
var merge = require('merge');

var PluginError = gutil.PluginError;

module.exports = function (opt) {
  function replaceExtension(path) {
    path = path.replace(/\.coffee\.md$/, '.litcoffee');
    return gutil.replaceExtension(path, '.js');
  }

  function transform(file, enc, cb) {
    if (file.isNull()) return cb(null, file);
    if (file.isStream()) return cb(new PluginError('gulp-coffee', 'Streaming not supported'));

    var data;
    var str = file.contents.toString('utf8');  // 1、 ，str ， ！
    var dest = replaceExtension(file.path);

    var options = merge({  // 2、 
      bare: false,
      coffee: require('coffeescript'),
      header: false,
      sourceMap: !!file.sourceMap,
      sourceRoot: false,
      literate: /\.(litcoffee|coffee\.md)$/.test(file.path),
      filename: file.path,
      sourceFiles: [file.relative],
      generatedFile: replaceExtension(file.relative)
    }, opt);

    try {
      data = options.coffee.compile(str, options);
    } catch (err) {
      return cb(new PluginError('gulp-coffee', err));
    }

    if (data && data.v3SourceMap && file.sourceMap) {
      applySourceMap(file, data.v3SourceMap);
      file.contents = new Buffer(data.js);   
    } else {
      file.contents = new Buffer(data);      // 3、 buffer 
    }

    file.path = dest;
    cb(null, file);                              //  4、 
  }

  return through.obj(transform);
};