How to exclude some code when building for production?

[samadadi]

I am using and importing msw library in my code as an es module in development mode & I am using import.meta.env.DEV to include this in just development. But when I am building for production this library is also included in the build output. So how to exclude this code from build output?

[adamlindqvist]

@samadadi

I'm doing it like this to exclude msw from the production bundle:

// index.tsx

async function prepare() {
    if (import.meta.env.DEV) {
        const { worker } = await import('./mocks/browser');

        return worker.start();
    }
}

prepare().then(() => {
    ReactDOM.render(
        <React.StrictMode>
            <App />
        </React.StrictMode>,
        document.getElementById('root')
    );
});

[florianmatz]

Which - is as I just found out - a problem for Playwright / Cypress if you have to assign window.msw = {}... or something, because the promise is not resolved, when E2E testing starts...

[apdrsn]

@florianmatz did you find a solution to this issue?

[cchangwen]

such as if(false) { } will be removed too.

[hassaannoor]

How do you do this in case of export statements. I'm in need of excluding the export of POST function during production in a svelte endpoint.

// +page.server.ts
export async function POST({ params, request }) {
...
}