What does systemjs.config.js do in angular 2 packaging structure?
<p>And also what does var map,packages, var config do here  I am bit confused here 
do they do any config.I seen every project and I found everywhere they put this file. What this function do?    </p>

<pre><code> (function(global) {

      // map tells the System loader where to look for things
      var map = {
        'app':                        'app', // 'dist',
        'rxjs':                       'node_modules/rxjs',
        'angular2-in-memory-web-api': 'node_modules/angular2-in-memory-web-api',
        '@angular':                   'node_modules/@angular',
    'primeng':                        'node_modules/primeng'
      };

      // packages tells the System loader how to load when no filename and/or no extension
      var packages = {
        'app':                        { main: 'boot.js',  defaultExtension: 'js' },
        'rxjs':                       { defaultExtension: 'js' },
        'angular2-in-memory-web-api': { defaultExtension: 'js' },
        'primeng':                    { defaultExtension: 'js' }
      };

      var packageNames = [
        '@angular/common',
        '@angular/compiler',
       //
      ];

      // add package entries for angular packages in the form '@angular/common': { main: 'index.js', defaultExtension: 'js' }
      packageNames.forEach(function(pkgName) {
        packages[pkgName] = { main: 'index.js', defaultExtension: 'js' };
      });

      var config = {
        map: map,
        packages: packages
      }

      // filterSystemConfig - index.html's chance to modify config before we register it.
      if (global.filterSystemConfig) { global.filterSystemConfig(config); }

      System.config(config);

    })(this);
</code></pre>