gulpfile.js

const gulp = require('gulp');
const { spawn } = require('child_process');

const watchedPaths = [
  'src/**/*.js',
  'src/**/*.graphql',
];

let node;

gulp.task('serve', ['lint'], function (cb) {
  if (node) node.kill();

  node = spawn('node', ['src/index.js'], { stdio: 'inherit' });
  node.on('close', function (code) {
    if (code === 8) {
      cb(code);
      console.log('Error detected, waiting for changes...');
    }
  });
  cb();
});

gulp.task('watch', function () {
  gulp.watch(watchedPaths, ['serve']);
});

gulp.task('lint', function (cb) {
  const lint = spawn('./node_modules/.bin/eslint', ['--cache', 'src'], { stdio: 'inherit' });
  lint.on('close', function (code) {
    if (code === 8) {
      cb(code);
      gulp.log('Error detected, waiting for changes...');
    }
    cb();
  });
});

gulp.task('default', ['watch', 'serve']);

// clean up if an error goes unhandled.
process.on('exit', function () {
  if (node) node.kill();
});