bundler.js

const fs = require('fs');
const path = require('path');
const babel = require('babel-core');
const babylon = require('babylon');
const traverse = require('babel-traverse').default;

let ID = 0;


function createAsset(filename) {
    const content = fs.readFileSync(filename, 'utf-8');

    const ast = babylon.parse(content, {
        sourceType: "module"
    });

    const dependencies = [];

    traverse(ast, {
        ImportDeclaration: ( {node} ) => {
            dependencies.push(node.source.value);
        }
    });

    let id = ID++;

    const {code} = babel.transformFromAst(ast, null, {
        presets: ['env'],
    })

    return {
        id,
        filename,
        dependencies,
        code
    };

}

function createGraph(entry) {
    const mainAsset = createAsset(entry);

    const queue = [mainAsset];

    for (const asset of queue) {
        const dirname = path.dirname(asset.filename)

        asset.mapping = {};

        asset.dependencies.forEach(relativePath => {
            const absolutePath = path.join(dirname, relativePath);

            const child = createAsset(absolutePath);

            asset.mapping[relativePath] = child.id;

            queue.push(child);
        });
    }

    return queue;
}

function bundle(graph) {

    let modules = '';

    graph.forEach((mod) => {
        modules += `${mod.id}: [
            function(require, module, exports) {
                ${mod.code}
            },
            ${JSON.stringify(mod.mapping)},
        ],`;
    });

    const result = `
        (function(modules) {
            function require(id) {
                const [fn, mapping] = modules[id];

                function localRequire(relativePath) {
                    return require(mapping[relativePath]);
                }

                const module = { exports: {} };

                fn(localRequire, module, module.exports);

                return module.exports;
            }

            require(0);
        })( {${modules}} )
    `;

    return result;

}

const graph = createGraph('./my-modules/entry.js');

const result = bundle(graph);

console.log(result);