Building a custom D3 with Smash and Gulp

gulpfile.es6

import path from 'path';
import fs from 'fs';
import { Readable } from 'stream';
import es from 'event-stream';
import gulp from 'gulp';
import smash from 'smash';

const SRC_DIR = path.resolve('./src');
const JAVASCRIPTS_SRC_DIR = path.join(SRC_DIR, JAVASCRIPTS_DIR);

// Build custom D3 version
// -----------------------

// We only need some modules of D3 and the modularization isn’t finished yet.
// See https://github.com/mbostock/d3/issues/2461
// Meanwhile we’re using smash for this purpose.
// See https://github.com/mbostock/smash/wiki
const D3_MODULES = [
  'start',
  'geo/path', 'geo/orthographic',
  'scale/quantile', 'scale/linear',
  'xhr/json', 'dsv/tsv',
  'end',
];
const D3_BUILD_FILE = path.join(JAVASCRIPTS_SRC_DIR, 'vendor', 'd3.js');
const D3_PRIMER = '/* Custom D3.js (http://d3js.org/) build created with `gulp d3` */\n/* eslint-disable */\n';

gulp.task('d3', () => {
  const primerStream = new Readable();
  primerStream.push(D3_PRIMER);
  primerStream.push(null);
  const d3Path = path.dirname(require.resolve('d3'));
  const modules = D3_MODULES.map((module) =>
    path.join(d3Path, 'src', module + '.js')
  );
  const smashStream = smash(modules);
  return es.merge(primerStream, smashStream)
    .pipe(fs.createWriteStream(D3_BUILD_FILE));
});