How to build react app each time when code is modified

Question

I have standard react application created by CRA(create-react-app), I have added craco to setup webpack aliases,

I want to create start script different from default one I want to create new build file each time code saved, to clarify more I want to build my project each time I save it while writing code, (I am doing that for nginx server);

Thats my craco config

const path = require('path');

module.exports = {
    webpack: {
        alias: {
            '@src': path.resolve(__dirname, 'src'),
        },
    },
};

I have tried several configurations for Craco bot nothing worked