How do you implement a custom module bundler in Node.js?

Question

Accepted Answer

**Module bundler** — combine multiple files into one.

```javascript
const fs = require("fs");
const path = require("path");

class SimpleBundler {
    constructor(entry) {
        this.entry = entry;
        this.modules = new Map();
        this.queue = [entry];
    }

async bundle() {
        while (this.queue.length > 0) {
            const modulePath = this.queue.shift();
            if (this.modules.has(modulePath)) continue;

const code = fs.readFileSync(modulePath, "utf8");
            const dependencies = this.extractDependencies(code, modulePath);

this.modules.set(modulePath, { code, dependencies });
            dependencies.forEach(dep => this.queue.push(dep));
        }

return this.generateBundle();
    }

extractDependencies(code, filePath) {
        const regex = /require$["'](.+?)["']$/g;
        const deps = [];
        let match;

while ((match = regex.exec(code)) !== null) {
            const depPath = path.resolve(path.dirname(filePath), match[1]);
            deps.push(depPath);
        }

return deps;
    }

generateBundle() {
        const modules = [];
        this.modules.forEach((module, id) => {
            modules.push(`"${id}": function(module, exports, require) {
                ${module.code}
            }`);
        });

return `
(function(modules) {
    function require(id) {
        const module = { exports: {} };
        modules[id](module, module.exports, require);
        return module.exports;
    }
    require("${this.entry}");
})({
    ${modules.join(",\n")}
});
`;
    }
}

// Usage
const bundler = new SimpleBundler("./src/index.js");
const bundle = await bundler.bundle();
fs.writeFileSync("dist/bundle.js", bundle);
```

Node.js: How do you implement a custom module bundler in Node.js?