old_contents: 'use strict';
  
  
  const Promise  = require('bluebird');
  
  
  module.exports = function (context) {
    return Promise.resolve().then(() => {
      const UglifyJS = require('uglify-js');
  
      let result = UglifyJS.minify(context.asset.source, {
        // turn off side effects to prevent uglify from simplifying
        // "browser-pack/prelude.js" IIFE down to a constant
        compress: { side_effects: false }
      });
  
      if (result.error) throw result.error;
  
      // Special case for "browser-pack/prelude.js": if source will be empty after
      // compression - skip compression, because file may be included by macros.
      if (result.code !== '') {
        context.asset.source = result.code;
      }
    });
  };
  
new_contents: 'use strict';
  
  
  const Promise  = require('bluebird');
  
  
  module.exports = function (context) {
    return Promise.resolve().then(() => {
      const UglifyJS = require('uglify-js');
  
      let result = UglifyJS.minify(context.asset.source, {
        // prevent simplifying "browser-pack/prelude.js" when used in a macros
        compress: { expression: true }
      });
  
      if (result.error) throw result.error;
  
      // Special case for "browser-pack/prelude.js": if source will be empty after
      // compression - skip compression, because file may be included by macros.
      if (result.code !== '') {
        context.asset.source = result.code;
      }
    });
  };
  
subject: Fix minification issue (again)