Webpack ENV setup

app.handlebars

<form action="{{MY_URL}}/purchase" method="post">
</form>

app.js

import appTemplate from 'app.handlebars'
document.body.insertAdjacentHTML('afterbegin', appTemplate({
    MY_URL: MY_URL
}));

local.js

module.exports = {
    MY_URL: JSON.stringify('http://localhost:3000')
};

prod.js

module.exports = {
    MY_URL: JSON.stringify('http://backend.example.com')
};

webpack.config.js

const webpack = require('webpack');
const path = require('path');

const config = (env) => {
    return {
        more_stuff: 'things',

        plugins: [
            new webpack.DefinePlugin(require(path.join(__dirname, env)))
        ]
    }
};

module.exports = config(process.env.NODE_ENV || 'local');