How to use the @jupyterlab/buildutils.Build.ensureAssets function in @jupyterlab/buildutils

var Build = require('@jupyterlab/buildutils').Build;

// Ensure a clear build directory.
var buildDir = './build';
if (fs.existsSync(buildDir)) {
  fs.removeSync(buildDir);
}
fs.ensureDirSync(buildDir);

fs.copySync('./package.json', './build/package.json');

// Handle the extensions.
var jlab = package_data.jupyterlab;
var extensions = jlab.extensions;
var mimeExtensions = jlab.mimeExtensions;
Build.ensureAssets({
  packageNames: Object.keys(mimeExtensions).concat(Object.keys(extensions)),
  output: jlab.outputDir
});

// Create the entry point file.
var source = fs.readFileSync('index.js').toString();
var template = Handlebars.compile(source);
var data = {
  jupyterlab_extensions: extensions,
  jupyterlab_mime_extensions: mimeExtensions,
};
var result = template(data);

fs.writeFileSync(path.resolve(buildDir, 'index.out.js'), result);

// Copyright (c) Jupyter Development Team.
// Distributed under the terms of the Modified BSD License.

var data = require('./package.json');
var Build = require('@jupyterlab/buildutils').Build;

var names = Object.keys(data.dependencies).filter(function (name) {
  var packageData = require(name + '/package.json');
  return packageData.jupyterlab !== undefined;
});

var extras = Build.ensureAssets({
  packageNames: names,
  output: './build'
});

module.exports = [
  {
    entry: ['whatwg-fetch', './index.js'],
    output: {
      path: __dirname + '/build',
      filename: 'bundle.js'
    },
    node: {
      fs: 'empty'
    },
    bail: true,
    devtool: 'source-map',

// Copyright (c) Jupyter Development Team.
// Distributed under the terms of the Modified BSD License.
var data = require('./package.json');
var Build = require('@jupyterlab/buildutils').Build;

var names = Object.keys(data.dependencies).filter(function(name) {
  var packageData = require(name + '/package.json');
  return packageData.jupyterlab !== undefined;
});

var extras = Build.ensureAssets({
  packageNames: names,
  output: './build'
});

module.exports = [
  {
    entry: ['whatwg-fetch', './index.js'],
    output: {
      path: __dirname + '/build',
      filename: 'bundle.js'
    },
    node: {
      fs: 'empty'
    },
    bail: true,
    devtool: 'cheap-source-map',

|----------------------------------------------------------------------------*/

var path = require('path');
var fs = require('fs-extra');
var Handlebars = require('handlebars');
var HtmlWebpackPlugin = require('html-webpack-plugin');
var webpack = require('webpack');

var Build = require('@jupyterlab/buildutils').Build;
var package_data = require('./package.json');

// Handle the extensions.
var jlab = package_data.jupyterlab;
var extensions = jlab.extensions;
var mimeExtensions = jlab.mimeExtensions;
Build.ensureAssets({
  packageNames: Object.keys(mimeExtensions).concat(Object.keys(extensions)),
  output: jlab.outputDir
});

fs.ensureDirSync('node_modules/codemirror/mode/prolog');
fs.copySync(path.join(path.resolve(jlab.buildDir),'../../../kernels/yap_kernel/prolog.js'), 'node_modules/codemirror/mode/prolog/prolog.js');
fs.copySync(path.join(path.resolve(jlab.buildDir),'../../../kernels/yap_kernel/meta.js'), 'node_modules/codemirror/mode/meta.js');

// Create the entry point file.
var source = fs.readFileSync('index.js').toString();
var template = Handlebars.compile(source);
var data = {
  jupyterlab_extensions: extensions,
  jupyterlab_mime_extensions: mimeExtensions,
};
var result = template(data);

// Copyright (c) Jupyter Development Team.
// Distributed under the terms of the Modified BSD License.
var data = require('./package.json');
var Build = require('@jupyterlab/buildutils').Build;

var names = Object.keys(data.dependencies).filter(function(name) {
  var packageData = require(name + '/package.json');
  return packageData.jupyterlab !== undefined;
});

var extras = Build.ensureAssets({
  packageNames: names,
  output: './build'
});

module.exports = [
  {
    entry: ['whatwg-fetch', './index.js'],
    output: {
      path: __dirname + '/build',
      filename: 'bundle.js'
    },
    node: {
      fs: 'empty'
    },
    bail: true,
    devtool: 'source-map',

// Handle the extensions.
var jlab = package_data.jupyterlab;
var extensions = jlab.extensions;
var mimeExtensions = jlab.mimeExtensions;
var packageNames = Object.keys(mimeExtensions).concat(Object.keys(extensions));

// Ensure a clear build directory.
var buildDir = plib.resolve(jlab.buildDir);
if (fs.existsSync(buildDir)) {
  fs.removeSync(buildDir);
}
fs.ensureDirSync(buildDir);

// Build the assets
var extraConfig = Build.ensureAssets({
  packageNames: packageNames,
  output: jlab.outputDir
});

// Create the entry point file.
var source = fs.readFileSync('index.js').toString();
var template = Handlebars.compile(source);
var data = {
  jupyterlab_extensions: extensions,
  jupyterlab_mime_extensions: mimeExtensions
};
var result = template(data);

fs.writeFileSync(plib.join(buildDir, 'index.out.js'), result);
fs.copySync('./package.json', plib.join(buildDir, 'package.json'));
fs.copySync(

var fs = require('fs-extra');
var Handlebars = require('handlebars');
var HtmlWebpackPlugin = require('html-webpack-plugin');
var webpack = require('webpack');
var DuplicatePackageCheckerPlugin = require('duplicate-package-checker-webpack-plugin');
var Visualizer = require('webpack-visualizer-plugin');

var Build = require('@jupyterlab/buildutils').Build;
var package_data = require('./package.json');

// Handle the extensions.
var jlab = package_data.jupyterlab;
var extensions = jlab.extensions;
var mimeExtensions = jlab.mimeExtensions;

var extraConfig = Build.ensureAssets({
  packageNames: Object.keys(mimeExtensions).concat(Object.keys(extensions)),
  output: jlab.outputDir
});

// Create the entry point file.
var source = fs.readFileSync('index.js').toString();
var template = Handlebars.compile(source);
var data = {
  jupyterlab_extensions: extensions,
  jupyterlab_mime_extensions: mimeExtensions
};
var result = template(data);

// Ensure a clear build directory.
var buildDir = path.resolve(jlab.buildDir);
if (fs.existsSync(buildDir)) {

var path = require('path');
var fs = require('fs-extra');
var Handlebars = require('handlebars');
var HtmlWebpackPlugin = require('html-webpack-plugin');
var webpack = require('webpack');
var DuplicatePackageCheckerPlugin = require('duplicate-package-checker-webpack-plugin');

var Build = require('@jupyterlab/buildutils').Build;
var package_data = require('./package.json');

// Handle the extensions.
var jlab = package_data.jupyterlab;
var extensions = jlab.extensions;
var mimeExtensions = jlab.mimeExtensions;
Build.ensureAssets({
  packageNames: Object.keys(mimeExtensions).concat(Object.keys(extensions)),
  output: jlab.outputDir
});

// Create the entry point file.
var source = fs.readFileSync('index.js').toString();
var template = Handlebars.compile(source);
var data = {
  jupyterlab_extensions: extensions,
  jupyterlab_mime_extensions: mimeExtensions
};
var result = template(data);

// Ensure a clear build directory.
var buildDir = path.resolve(jlab.buildDir);
if (fs.existsSync(buildDir)) {

}

  // Handle extensions.
  ['extension', 'mimeExtension'].forEach(function(item) {
    var ext = jlab[item];
    if (ext === true) {
      ext = ''
    }
    if (typeof ext !== 'string') {
      return;
    }
    corePackage.jupyterlab[item + 's'][data.name] = ext;
  });
});

Build.ensureAssets({
  packageNames: Object.keys(corePackage.jupyterlab.extensions),
  output: '.'
});

// Write the package.json back to disk.
var text = JSON.stringify(sortPackageJson(corePackage), null, 2) + '\n';
fs.writeFileSync('./package.json', text);

var data = require('./package.json');
var Build = require('@jupyterlab/buildutils').Build;

var names = Object.keys(data.dependencies).filter(function(name) {
  var packageData = require(name + '/package.json');
  return packageData.jupyterlab !== undefined;
});

Build.ensureAssets({
  packageNames: names,
  output: './build'
});