Angular2 ReferenceError：未定义包

Question

我使用Angular2创建了小应用程序，我在Chrome浏览器中遇到以下错误：

zone.js:323 Error: ReferenceError: packages is not defined
    at materialComponents.forEach.name (http://localhost:4200/system-config.js:17:5)
    at Array.forEach (native)
    at eval (http://localhost:4200/system-config.js:16:20)
Evaluating http://localhost:4200/system-config.js
Error loading http://localhost:4200/system-config.js

基本上，这个错误发生在以下代码上。

系统config.ts

/** Map relative paths to URLs. */
const map: any = {
'@angular2-material': 'vendor/@angular2-material',   // created in vendor directory
'ng2-material': 'vendor/ng2-material',    
'moment': 'vendor/moment/moment.js'
};

/** User packages configuration. */
const packages: any = {};

// Material Components
const materialComponents = [
    'core',
    'checkbox',
    'input',
    'progress-bar',
    'progress-circle',
    'radio',
    'sidenav',
    'slide-toggle',
    'toolbar'
];

materialComponents.forEach(name => {                //Here it says package not defined
    packages[`@angular2-material/${name}`] = {
       format: 'cjs',
       defaultExtension: 'js',
       main: name + '.js'
     };
});

由于