A small project I started make use a node module (installed via npm) that declares const variables. Running and testing this project is well, but browserify fails when UglifyJS is executed.

Unexpected token: keyword (const)

Here is a generic Gulp file that I have successfully been using for a few other past projects without this issue (i.e. without that particular node module).

gulpfile.js

'use strict';



const browserify = require('browserify');

const gulp = require('gulp');

const source = require('vinyl-source-stream');

const derequire = require('gulp-derequire');

const buffer = require('vinyl-buffer');

const uglify = require('gulp-uglify');

const sourcemaps = require('gulp-sourcemaps');

const gutil = require('gulp-util');

const path = require('path');

const pkg = require('./package');

const upperCamelCase = require('uppercamelcase');



const SRC_PATH = path.dirname(pkg.main);

const DIST_PATH = path.dirname(pkg.browser);



const INPUT_FILE = path.basename(pkg.main);

const OUTPUT_FILE = path.basename(pkg.browser);



const MODULE_NAME = upperCamelCase(pkg.name);





gulp.task('default', () => {

  // set up the browserify instance on a task basis

  var b = browserify({

    entries: INPUT_FILE,

    basedir: SRC_PATH,

    transform: ['babelify'],

    standalone: MODULE_NAME,

    debug: true

  });



  return b.bundle()

    .pipe(source(OUTPUT_FILE))

    .pipe(buffer())

    .pipe(derequire())

    .pipe(sourcemaps.init({loadMaps: true}))

    .pipe(uglify())

    .on('error', gutil.log)

    .pipe(sourcemaps.write('.'))

    .pipe(gulp.dest(DIST_PATH))

  ;

});

I have tried fixing this by replace all const to var in that npm-installed module, and everything is fine. So I do not understand the failure.

What's wrong with const? Unless someone uses IE10, all major browsers support this syntax.

Is there a way to fix this without requiring a change to that node module?

Update

I have temporarily (or permanently) replaced UglifyJS with Butternut and seem to work.