Chrome debugger not supported

Chrome debugger not supported if I put breakpoint on 'alert' in snippet below:
<pre>
 <script type="text/typescript">
  //import "./common.js"//too ambitious, it says 'Uncaught ReferenceError: exports is not defined'
  let message:string = 'It worked???'
//I try to put a breakpoint here...  'debugger' keyword works though
alert(message)
</script>
</pre>