title: Using JS extension by default in module import in typescript
body: <p>I am trying to import a typescript module into another file using system.js but I have to specify the js extension at the time of import.</p>
  
  <p>This is my app.ts file</p>
  
  <pre><code>import {PI, calculateCircumference} from "./math/circle.js";
  console.log(PI);
  console.log(calculateCircumference(10));
  </code></pre>
  
  <p>Index.html</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html lang="en"&gt;
  &lt;head&gt;
      &lt;meta charset="UTF-8"&gt;
      &lt;title&gt;Learning Typescript&lt;/title&gt;
      &lt;script src="node_modules/systemjs/dist/system.js"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
  &lt;script&gt;
      System.import('/app.js');
  &lt;/script&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>When I try to use the following code in index.html</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html lang="en"&gt;
  &lt;head&gt;
      &lt;meta charset="UTF-8"&gt;
      &lt;title&gt;Learning Typescript&lt;/title&gt;
      &lt;script src="node_modules/systemjs/dist/system.js"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
  &lt;script&gt;
      System.config({
          baseURL : '/',
          defaultJSExtensions : true
      });
      System.import('/app.js');
  &lt;/script&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>TypeError: System.config is not a function</p>
  
  <p>Where am I going wrong?</p>
  
  <p>This is my packages.json file</p>
  
  <pre><code>{
    "name": "typescript",
    "version": "1.0.0",
    "main": "index.js",
    "scripts": {
      "test": "echo \"Error: no test specified\" &amp;&amp; exit 1",
      "start": "lite-server"
    },
    "author": "",
    "license": "ISC",
    "devDependencies": {
      "lite-server": "^2.4.0"
    },
    "dependencies": {
      "browser-sync": "^2.26.3",
      "systemjs": "^2.0.2"
    },
    "keywords": [],
    "description": ""
  }
  </code></pre>