closureCompilerPromise.js

'use strict';

const

  querystring = require('querystring'),
  http = require('http'),

  /**
   * Converts options and buffer arguments into a proper data object.
   * @param  {!Object} options           Google Closure Compiler options
   * @return {function(!string): Object} Function that assembles data based on specific buffer
   */
  assembleData = options => buffer => querystring.stringify({
    'js_code' : buffer,

    'compilation_level' : !!options.compilationLevel ? options.compilationLevel : 'ADVANCED_OPTIMIZATIONS',
    'output_format'     : !!options.outputFormat ? options.outputFormat         : 'json',
    'output_info'       : !!options.outputInfo ? options.outputInfo             : ['compiled_code','warnings','errors','statistics'],
    'warning_level'     : !!options.warningLevel ? options.warningLevel         : 'VERBOSE',

    'language' : 'ECMASCRIPT6_STRICT'
  }),

  /**
   * Converts compiler data into html request options
   * @param  {!Object}
   * @return {Object}
   */
  assembleRequestOptions = assembledData => ({
    host: 'closure-compiler.appspot.com',
    port: '80',
    path: '/compile',
    method: 'POST',
    headers: {
      'Content-Type': 'application/x-www-form-urlencoded',
      'Content-Length': Buffer.byteLength(assembledData)
    }
  });

/**
 * Google Closure Compiler
 * @param  {string}  buffer
 * @param  {!Object} options
 * @return {promise}
 */
module.exports = ( buffer , options ) => new Promise( ( resolve , reject ) => {

  let result = '';

  const
    assembledData = assembleData(options)(buffer),
    request = http.request( assembleRequestOptions(assembledData) , response => {

      response.setEncoding('utf8');

      response.on('data' , data => {
        result += data;
      } );

      response.on('end', () => resolve(JSON.parse(result)) );

    } );

    request.on('error', error => reject(error) );

    request.write(assembledData);
    request.end();

} );