How to differentiate between Svelte dev mode and build mode?

Question

The dev mode using npm run dev, the release mode using npm build

How could i know that it's currently built on dev mode or not in the code, for example:

<script>
    import {onMount} from 'svelte';

    onMount(function(){
        if(DEVMODE) { // --> what's the correct one?
            console.log('this is x.svelte');
        }
    })
</script>
 

Answer 1

Not sure about the correct method. I share what I did on my project.

1. in rollup.config.js

import replace from "@rollup/plugin-replace";
const production = !process.env.ROLLUP_WATCH;

2. inside plugins:[ ] block add this

replace({
          isProduction: production,
      }),

rollup.config.js will look like this.

},
    plugins: [
        replace({
            isProduction: production,
        }),
        svelte({
            

3. Then use isProduction inside components .

if (!isProduction){ console.log('Developement Mode'); }

Answer 2

If you are using sveltekit:

import { dev } from '$app/env';

if (dev) {
    //do in dev mode
}