What is mean by System.register in JS file?

Question

What is mean by System.register in JS file, while using directives in angular 2.

Answer 1

I think this question is not specific to directives in angular2, it is general question about ES6, TypeScript and other modern compilers which use SystemJS. The short answer - it is wrapper created by System.js to isolate code and inject external dependencies.

This code:

  import { p as q } from './dep';

  var s = 'local';

  export function func() {
    return q;
  }

  export class C {
  }

Will generate:

System.register(['./dep'], function($__export, $__moduleContext) {
 var s, C, q;
 function func() {
   return q;
 }
 $__export('func', func);
 return {
   setters: [
   // every time a dependency updates an export, 
   // this function is called to update the local binding
   // the setter array matches up with the dependency array above
   function(m) {
     q = m.p;
   }
   ],
   execute: function() {
     // use the export function to update the exports of this module
     s = 'local';
     $__export('C', C = $traceurRuntime.createClass(...));
     var moduleName = $__moduleContext.id;
   }
 };
});

Here - System register you can find more detail inforamtion about thins question.