Svelte Webpack Demo

See it live here

Add svelte globally

module.exports = {
    ...
    entry: {
        svelte: {
            import: './node_modules/svelte/src/index-client.js',
            library: {
                name: 'svelte',
                type: 'global'
            }
        }
        ...
    },
    ...
};

Setup loader

Add the svelte-loader

module.exports = {
    ...
    module: {
        rules: [
            {
                test: /\.(svelte|svelte\.js)$/,
                use: 'svelte-loader'
            },
            {
                // required to prevent errors from Svelte on Webpack 5+, omit on Webpack 4
                test: /node_modules\/svelte\/.*\.mjs$/,
                resolve: {
                    fullySpecified: false
                }
            }
        ]
    },
    resolve: {
        extensions: ['.json', '.js', '.jsx', '.svelte'],
        conditionNames: ['svelte']
    }
    ...
}

Create component and entrypoint

In src/Counter.svelte, let's define the following:

<script>
    export let count = 0;

    console.log("Counter loaded!");

    export function handleClick() {
        count += 1;
        return count;
    }

    export const getCount = () => count;
</script>

<button class="counter btn btn-primary" on:click={handleClick}>
    clicks: {count}
</button>

And, we'll have the bundler make us a .js distributable:

module.exports = {
    ...
    entry:{
        Counter: {
            import: './src/Counter.svelte',
            library: {
                name: 'Counter',
                type: 'global'
            }
        }
    }
    ...
}

Change webpack optimizations

Since we have multiple entrypoints that will have overlap (e.g., svelte internals in this case), we will use a single runtime. The runtime in Webpack takes care of loading for us.

module.exports = {
    ...
    optimization: {
        runtimeChunk: 'single'
    },
    ...
};

If you skip this step, you will get an obscure error along the lines of: Uncaught TypeError: Cannot read properties of undefined (reading 'call')

Load bundles

<script src="dist/runtime.js"></script>
<script src="dist/svelte.js"></script>
<script src="dist/Counter.js"></script>

Mount component

After the scripts above, add:

<script>
    const container = document.getElementById('counter-container')
    const counter = svelte.mount(Counter,
        {
            target: container,
            props: {
                count: 1
            }
        }
    );
</script>

Notice, we initialized the count to 1 by providing it as a property.

Profit

The steps outlined here are usable for other bundlers too. The setup difficulty is less burdensome the technical debt and maintenance headache of glue logic.