[2278] Production build is not happend with express

Here is my express.js code for render nuxt in server side

process.env.NODE_ENV = 'production'; const isProd = process.env.NODE_ENV === 'production'; let config = require('../nuxt.config.js') const nuxt = new Nuxt(config); // No build in production if (!isProd) { const builder = new Builder(nuxt) builder.build() } app.use(nuxt.render);

But when i run in production mode build is not happening