Watch default Task

gulpfile.js

/**
  * Watch Tasks.
  *
  * Watches for file changes and runs specific tasks.
  */

 gulp.task( 'default', [ 'styles', 'vendorsJs', 'customJS' ], function () {
 	gulp.watch( './assets/css/**/*.scss', [ 'styles' ] );
 	gulp.watch( './assets/js/vendors/*.js', [ 'vendorsJs' ] );
 	gulp.watch( './assets/js/custom/*.js', [ 'customJS' ] );
 });