index.js

var SplitByNamePlugin = module.exports = function (options) {
  this.options = options;

  // process buckets
  this.options.buckets = this.options.buckets.slice(0).map(function (bucket) {
    if (!(bucket.regex instanceof RegExp)) {
      bucket.regex = new RegExp(bucket.regex);
    }
    return bucket;
  });
};

SplitByNamePlugin.prototype.apply = function(compiler) {
  var options = this.options;

  function findMatchingBucket(chunk) {
    var match = null;
    options.buckets.some(function (bucket) {
      if (bucket.regex.test(chunk.rawRequest)) {
        match = bucket;
        return true;
      }
    });
    return match;
  }

  compiler.plugin("compilation", function(compilation) {
    var extraChunks = {};

    // Find the chunk which was already created by this bucket.
    // This is also the grossest function name I've written today.
    function bucketToChunk(bucket) {
      return extraChunks[bucket.name];
    }

    compilation.plugin("optimize-chunks", function(chunks) {
      var addChunk = this.addChunk.bind(this);
      chunks
        // only parse the entry chunk
        .filter(function (chunk) {
          return chunk.entry;
        })
        .forEach(function(chunk) {
          chunk.modules.slice().forEach(function (mod) {
            var bucket = findMatchingBucket(mod),
                newChunk;
            if (!bucket) {
              // it stays in the original bucket
              return;
            }
            if (!(newChunk = bucketToChunk(bucket))) {
              newChunk = extraChunks[bucket.name] = addChunk(bucket.name);
            }
            // add the module to the new chunk
            newChunk.addModule(mod);
            mod.addChunk(newChunk);
            // remove it from the existing chunk
            mod.removeChunk(chunk);
          });

          options.buckets
            .map(bucketToChunk)
            .filter(Boolean)
            .concat(chunk)
            .forEach(function (chunk, index, allChunks) { // allChunks = [bucket0, bucket1, .. bucketN, orig]
              if (index) { // not the first one, they get the first chunk as a parent
                chunk.parents = [allChunks[0]];
              } else { // the first chunk, it gets the others as 'sub' chunks
                chunk.chunks = allChunks.slice(1);
              }
              chunk.initial = chunk.entry = !index;
            });
        });
    });
  });
};