Task never defined: minify-js

Question

This is my gulpfile.js,

 gulp.task('concat-js',gulp.series('compile-css','minify-js'), function() {
  return gulp.src(['ui/build/**/*.js'],{"base":"./ui/build/"})
    .pipe(order([
    'ui-app.js',
    'aacoc_charts/chartsModule.js',
    '**/*.js'
    ]))
    .pipe(concatJs('application.js'))
    .pipe(gulp.dest('./ui/build'));
});

This is the version of gulp, CLI version: 2.2.0 Local version: 4.0.2

But while running npm install" I am getting this error 'AssertionError [ERR_ASSERTION]: Task never defined: minify-js'

Can you please help me on this