wails/v2/internal/frontend/runtime/dev/build.js

/* jshint esversion: 8 */

let sveltePlugin = {
    name: 'svelte',
    setup(build) {
        let svelte = require('svelte/compiler');
        let path = require('path');
        let fs = require('fs');

        build.onLoad({filter: /\.svelte$/}, async (args) => {
            // This converts a message in Svelte's format to esbuild's format
            let convertMessage = ({message, start, end}) => {
                let location;
                if (start && end) {
                    let lineText = source.split(/\r\n|\r|\n/g)[start.line - 1];
                    let lineEnd = start.line === end.line ? end.column : lineText.length;
                    location = {
                        file: filename,
                        line: start.line,
                        column: start.column,
                        length: lineEnd - start.column,
                        lineText,
                    };
                }
                return {text: message, location};
            };

            // Load the file from the file system
            let source = await fs.promises.readFile(args.path, 'utf8');
            let filename = path.relative(process.cwd(), args.path);

            // Convert Svelte syntax to JavaScript
            try {
                let {js, warnings} = svelte.compile(source, {filename});
                let contents = js.code + `//# sourceMappingURL=` + js.map.toUrl();
                return {contents, warnings: warnings.map(convertMessage)};
            } catch (e) {
                return {errors: [convertMessage(e)]};
            }
        });
    }
};

require('esbuild').build({
    minify: true,
    entryPoints: ['main.js'],
    bundle: true,
    outfile: '../ipc_websocket.js',
    plugins: [sveltePlugin],
}).catch(() => process.exit(1));