A simplified and annotated example of how JavaScript is loaded in the bundle by webpack.

Webpack-Bundle-Logic-Simplified.js

/**
 * In this simplified example,
 * '_application.js' is our entry point
 * and it requires 'init.js',
 * which in turn requires both the 'home_view'
 * and the 'current_user_model'
 */

var modules = [
  // dependencies can be referenced by index
  function() { 
    //... contents of ‘_application.js’ 
  },
  function() { 
    //... contents of ‘init.js’ 
  },
  function() { 
    //... contents of ./views/home_view.js’
  },
  function() { 
    //... contents of ./models/current_user_model.js’
  },
];

// This function gets called right away
// with the modules above as a parameter.
(function(modules) {
  // The module cache
  var installedModules = {};
  
  // The require function
  function __webpack_require__(moduleId) {
    // Check if module is in cache
    if(installedModules[moduleId])  
      return installedModules[moduleId].exports; 
    
    // If the module isn't in the cache -  
    // Create a new module (and put it into the cache)
    var module = installedModules[moduleId] = {
      exports: {},
      id: moduleId,
      loaded: false
    };
    
    // Execute the module function
    // Meaning the method at index 'moduleId'
    // in the 'modules' array gets called
    // with access to the 'module', 'module.exports',
    // and using '__webpack_require__'
    // wherever your script called 'require'
    modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
    
    // Flag the module as loaded
    module.loaded = true;
    
    // Return the exports of the module
    return module.exports;
  };
  
  // ...
  
  // Load entry module and return exports
  // Meaning this will run '__webpack_require__'
  // with index 0 of the modules array
  return __webpack_require__(0);
})(modules);