Update your systemjs.config.js file with the following changes:

(function (global) {
  System.config({
    map: {
      'rxjs': 'node_modules/rxjs',
      '@angular': 'node_modules/@angular',
     'app': './app',
     'angular2-in-memory-web-api' : 'node_modules/angular2-in-memory-web-api'
   },
    packages: {
      'app': {
        main: 'main.js',
        defaultExtension: 'js'
      },

      '@angular/platform-browser': {
        main: 'bundles/platform-browser.umd.js'
      },

      '@angular/core': {
        main: 'bundles/core.umd.js'
      },

      '@angular/http': {
        main: 'bundles/http.umd.js'
      },

      '@angular/compiler': {
        main: 'bundles/compiler.umd.js'
      },

      '@angular/compiler-cli': {
        main: 'index.js'
      },

      '@angular/router': {
        main: 'bundles/router.umd.js'
      },

      '@angular/upgrade': {
        main: 'bundles/upgrade.umd.js'
      },

      '@angular/forms': {
        main: 'bundles/forms.umd.js'
      },

      '@angular/common': {
        main: 'bundles/common.umd.js',
        defaultExtension: 'js'
      },

      '@angular/platform-browser-dynamic': {
        main: 'bundles/platform-browser-dynamic.umd.js'
      },

      '@angular/platform-server': {
        main: 'bundles/platform-server.umd.js'
      },

      'rxjs': {
        defaultExtension: 'js'
      },

      'angular2-in-memory-web-api': {
        main: './index.js',
        defaultExtension: 'js'
      }
    }
  });
})(this);

It appears that the Angular.io team included systemjs-angular-loader.js in the Plunker links, but overlooked adding the file to downloadable projects.

Kindly ensure to add systemjs-angular-loader.js at the same level as systemjs.config.js

var templateUrlRegex = /templateUrl\s*:(\s*['"`](.*?)['"`]\s*)/gm;
var stylesRegex = /styleUrls *:(\s*\[[^\]]*?\])/g;
var stringRegex = /(['`"])((?:[^\\]\\\1|.)*?)\1/g;

module.exports.translate = function(load){

  var url = new URL(load.address);

  var basePathParts = url.pathname.split('/');

  if (url.href.indexOf('plnkr') != -1) {
    basePathParts.shift();
    basePathParts.shift();
  }

  basePathParts.pop();
  var basePath = basePathParts.join('/');
  load.source = load.source
    .replace(templateUrlRegex, function(match, quote, url){
      let resolvedUrl = url;

      if (url.startsWith('.')) {
        resolvedUrl = basePath + url.substr(1);
      }

      return `templateUrl: '${resolvedUrl}'`;
    })
    .replace(stylesRegex, function(match, relativeUrls) {
      var urls = [];

      while ((match = stringRegex.exec(relativeUrls)) !== null) {
        if (match[2].startsWith('.')) {
          urls.push(`'${basePath.substr(1)}${match[2].substr(1)}'`);
        } else {
          urls.push(`'${match[2]}'`);
        }
      }

      return "styleUrls: [" + urls.join(', ') + "]";
    });

  return load;
};

Source code retrieved from: https://angular.io/resources/live-examples/forms/ts/eplnkr.html

Have you heard about the new systemjs-angular-loader.js module mentioned in the Change Log for March 13th? I tried finding it at https://angular.io/docs/ts/latest/guide/change-log.html, but no luck so far.

Upon reviewing the error log, it is evident that the issue lies within the first few lines:

GET http://localhost:3000/systemjs-angular-loader.js 404 Not Found 2ms  zone.js (line 2019)

This indicates that the file systemjs-angular-loader.js is missing from your project.

In a response by @TimFogarty on Stack Overflow, it is mentioned that systemjs-angular-loader.js is a new addition in Angular 4.0.

Given that the official documentation does not provide clarity on the contents of systemjs-angular-loader.js and Angular-CLI does not generate it either, the recommended course of action would be to obtain it from the official Angular Quickstart project.

For reference, here is the current version of the file:

var templateUrlRegex = /templateUrl\s*:(\s*['"`](.*?)['"`]\s*)/gm;
var stylesRegex = /styleUrls *:(\s*\[[^\]]*?\])/g;
var stringRegex = /(['`"])((?:[^\\]\\\1|.)*?)\1/g;

module.exports.translate = function(load){
  if (load.source.indexOf('moduleId') != -1) return load;

  var url = document.createElement('a');
  url.href = load.address;

  var basePathParts = url.pathname.split('/');

  basePathParts.pop();
  var basePath = basePathParts.join('/');

  var baseHref = document.createElement('a');
  baseHref.href = this.baseURL;
  baseHref = baseHref.pathname;

  if (!baseHref.startsWith('/base/')) { // it is not karma
    basePath = basePath.replace(baseHref, '');
  }

  load.source = load.source
    .replace(templateUrlRegex, function(match, quote, url){
      var resolvedUrl = url;

      if (url.startsWith('.')) {
        resolvedUrl = basePath + url.substr(1);
      }

      return 'templateUrl: "' + resolvedUrl + '"';
    })
    .replace(stylesRegex, function(match, relativeUrls) {
      var urls = [];

      while ((match = stringRegex.exec(relativeUrls)) !== null) {
        if (match[2].startsWith('.')) {
          urls.push('"' + basePath + match[2].substr(1) + '"');
        } else {
          urls.push('"' + match[2] + '"');
        }
      }

      return "styleUrls: [" + urls.join(', ') + "]";
    });

  return load;
};

In my current Angular project, running version 4.3.2 which is not the latest, I discovered that systemjs-angular-loader.js is missing from my package.json file. Surprisingly, I did not encounter the 404 error mentioned by the original poster. Could it be that systemjs-angular-loader.js has been relocated within the updated versions of Angular (perhaps in the 4.x.y series)?

Interestingly, when I removed moduleId: module.id from the @Component decorator in my app.component.ts file, the page failed to load properly. This alteration seems to suggest a modification in the codebase, possibly alluded to in the documentation changelog provided at . Strangely, this change was not explicitly detailed in the official Angular Changelog at https://github.com/angular/angular/blob/master/CHANGELOG.md, nor in the Getting Started guide. Despite scouring the Angular documentation, I could not locate any examples showcasing the transition from the old method to the new one.

The solution to this mystery must lie within the official Angular code documentation, complete with clear before-and-after examples for developers to follow. Once identified, I will be sure to reference it here for others facing the same dilemma.