How to use the @microsoft/web-library-build.preCopy function in @microsoft/web-library-build

require('./tslint.json').rules
);

// Configure TypeScript.
build.TypeScriptConfiguration.setTypescriptCompiler(require('typescript'));
// Use css modules.
build.sass.setConfig({
  useCSSModules: true,
  moduleExportName: ''
});

// Use Karma Tests - Disable during develoment if prefered
build.karma.isEnabled = () => false;

// Disable unnecessary subtasks.
build.preCopy.isEnabled = () => false;

// Disable tslint
build.tslint.isEnabled = () => false;

// Only run bundling in production builds; this speeds up normal ci builds.
build.webpack.isEnabled = () => isProduction;

// Copy fabric-core to dist to be published with fabric-react.
build.postCopy.setConfig({
  shouldFlatten: false,
  copyTo: {
    [path.join(distFolder, 'sass')]: [
      'node_modules/office-ui-fabric-core/dist/sass/**/*.*'
    ],
    [path.join(distFolder, 'css')]: [
      'node_modules/office-ui-fabric-core/dist/css/**/*.*'

// });


// Always fail on test failures.
build.karma.setConfig({
  failBuildOnErrors: true
});

// Use css modules.
build.sass.setConfig({
  useCSSModules: true,
  moduleExportName: ''
});

// Copy fabric-core to dist to be published with fabric-react.
build.preCopy.setConfig({
  shouldFlatten: false,
  copyTo: {
    [path.join(distFolder, 'sass')]: [
      'node_modules/office-ui-fabric-core/dist/sass/**/*.*'
    ],
    [path.join(distFolder, 'css')]: [
      'node_modules/office-ui-fabric-core/dist/css/**/*.*'
    ]
  }
});

// Short aliases for subtasks.
build.task('webpack', build.webpack);
build.task('tslint', build.tslint);
build.task('ts', build.typescript);
build.task('sass', build.serial(build.preCopy, build.sass));

'use strict';

let path = require('path');
let build = require('@microsoft/web-library-build');

build.sass.setConfig({ useCSSModules: true });
build.webpack.setConfig({ configPath: null });

build.setConfig({
  libAMDFolder: path.join(build.getConfig().packageFolder, 'lib-amd'),
  libES6Folder: path.join(build.getConfig().packageFolder, 'lib-es6')
});

build.preCopy.cleanMatch = ['src/preCopyTest.ts'];

build.initialize(require('gulp'));