Different svelte variable value for npm run dev and npm run build - npm

Question

I'm developing a svelte+tailwind+PHP site with rollup.js. How can I set a variable in the svelte source files depending on if I'm running npm run dev or npm run build? I'd like the different builds to connect to different back-end servers.
This is my package.json in case that's relevant. I'm new to most of these tools, so please bear with me and correct me if I've misunderstood too much. After running npm run build, I run a script that scp's the build folder to the production server.
{
"name": "my-app",
"version": "1.0.0",
"scripts": {
"watch:tailwind": "postcss public/tailwind.css -o public/index.css -w",
"build:tailwind": "NODE_ENV=production postcss public/tailwind.css -o public/index.css",
"dev": "run-p autobuild watch:tailwind",
"build": "npm run build:tailwind && rollup -c",
"start": "sirv public --single --host",
"start:dev": "sirv public --single --dev",
"autobuild": "rollup -c -w"
},
"devDependencies": {
"#rollup/plugin-commonjs": "^16.0.0",
"#rollup/plugin-node-resolve": "^10.0.0",
"autoprefixer": "^10.0.4",
"d3-interpolate": "^2.0.1",
"npm-run-all": "^4.1.5",
"postcss": "^8.1.10",
"postcss-cli": "^8.3.0",
"postcss-nested": "^5.0.1",
"postcss-reporter": "^7.0.2",
"rollup": "^2.3.4",
"rollup-plugin-css-only": "^3.0.0",
"rollup-plugin-livereload": "^2.0.0",
"rollup-plugin-svelte": "^7.0.0",
"rollup-plugin-terser": "^7.0.0",
"svelte": "^3.0.0",
"svelte-dnd-action": "^0.6.22",
"svelte-loading-spinners": "^0.1.1",
"tailwindcss": "^2.0.1"
},
"dependencies": {
"sirv-cli": "^1.0.0"
}
}

Answer 1

You can use #rollup/plugin-replace:
A Rollup plugin which replaces strings in files while bundling.
plugins: [
replace({
// alternatively, one could pass process.env.NODE_ENV or 'development` to stringify
'process.env.NODE_ENV': JSON.stringify('production')
})
]