First, Install gulp and del to project directory locally

npm install --save-dev gulp del

Then add the clean task to your gulpfile.js

var gulp = require('gulp');
var del = require('del');

gulp.task('default', function() {
});

// Task to delete target build folder
gulp.task('clean', function() {
  return del(['public/**', '!public']);
});

gulp.task('default', ['clean']);

This task deletes all files in the public directory

The task in the code is added as a dependency for the 'default' task so every time default will run, clean will run before it.

You can also call the clean task manually by running the command:

gulp clean