old_contents: import gulp from 'gulp';
  import del from 'del';
  import eslint from 'gulp-eslint';
  import babel from 'gulp-babel';
  import sourcemaps from 'gulp-sourcemaps';
  import mocha from 'gulp-mocha';
  import istanbul from 'gulp-istanbul';
  import remapIstanbul from 'remap-istanbul/lib/gulpRemapIstanbul';
  
  
  gulp.task('clean', () => del(['lib/', 'test/', 'maps/', 'coverage/']));
  
  gulp.task('lint', () => {
    return gulp.src('src/**/*.js')
      .pipe(eslint())
      .pipe(eslint.format())
      .pipe(eslint.failAfterError());
  });
  
  gulp.task('build', ['clean'], () => {
    return gulp.src('src/lib/**/*.js')
      .pipe(sourcemaps.init())
      .pipe(babel())
      .pipe(sourcemaps.write('../maps', { includeContent: false, sourceRoot: '../src/lib' }))
      .pipe(gulp.dest('lib'));
  });
  
  gulp.task('build:test', ['build'], () => {
    return gulp.src('src/test/**/*.js')
      .pipe(babel())
      .pipe(gulp.dest('test'));
  });
  
  gulp.task('pre-test', ['build:test'], () => {
    return gulp.src(['lib/**/*.js'])
      .pipe(istanbul())
      .pipe(istanbul.hookRequire());
  });
  
  gulp.task('test', ['pre-test'], () => {
    return gulp.src(['test/**/*.js'])
      .pipe(mocha({ timeout: 10000 }))
      .pipe(istanbul.writeReports())
      .pipe(istanbul.enforceThresholds({ thresholds: { global: 50 } }));
  });
  
  
  gulp.task('remap-istanbul', ['test'], function () {
    return gulp.src('coverage/coverage-final.json')
      .pipe(remapIstanbul({
        reports: {
          'json': 'coverage/coverage.json',
          'html': 'coverage/lcov-report',
          'lcovonly': 'coverage/lcov.info'
        }
      }));
  });
  
  gulp.task('default', ['lint', 'test']);
  
new_contents: import gulp from 'gulp';
  import del from 'del';
  import eslint from 'gulp-eslint';
  import babel from 'gulp-babel';
  import sourcemaps from 'gulp-sourcemaps';
  import mocha from 'gulp-mocha';
  import istanbul from 'gulp-istanbul';
  import remapIstanbul from 'remap-istanbul/lib/gulpRemapIstanbul';
  
  
  gulp.task('clean', () => del(['lib/', 'test/', 'maps/', 'coverage/']));
  
  gulp.task('lint', () =>
    gulp.src(['src/**/*.js', 'gulpfile.babel.js'])
      .pipe(eslint())
      .pipe(eslint.format())
      .pipe(eslint.failAfterError())
  );
  
  gulp.task('build', ['clean'], () =>
    gulp.src('src/lib/**/*.js')
      .pipe(sourcemaps.init())
      .pipe(babel())
      .pipe(sourcemaps.write('../maps', { includeContent: false, sourceRoot: '../src/lib' }))
      .pipe(gulp.dest('lib'))
  );
  
  gulp.task('build:test', ['build'], () =>
    gulp.src('src/test/**/*.js')
      .pipe(babel())
      .pipe(gulp.dest('test'))
  );
  
  gulp.task('pre-test', ['build:test'], () =>
    gulp.src(['lib/**/*.js'])
      .pipe(istanbul())
      .pipe(istanbul.hookRequire())
  );
  
  gulp.task('test', ['pre-test'], () =>
    gulp.src(['test/**/*.js'])
      .pipe(mocha({ timeout: 10000 }))
      .pipe(istanbul.writeReports())
      .pipe(istanbul.enforceThresholds({ thresholds: { global: 50 } }))
  );
  
  
  gulp.task('remap-istanbul', ['test'], () =>
    gulp.src('coverage/coverage-final.json')
      .pipe(remapIstanbul({
        reports: {
          json: 'coverage/coverage.json',
          html: 'coverage/lcov-report',
          lcovonly: 'coverage/lcov.info',
        },
      }))
  );
  
  gulp.task('default', ['lint', 'test']);
  
subject: Fix codes detectd by ESLint