What happens when javascript fails?

What happens when javascript fails?

First off, I'm quite new to javascript and jquery. But in the past couple months I've come a long ways.

My question is basically this:

I've got an onload event setup on my body, which uses the PerformanceTiming features to log certain data. My understanding is PerformanceTiming only works with browsers supporting HTML5

What happens is a clients browser does not support HTML5?

Will it stop executing javascript once it hits the unrecognized code? What about the execution of different  javascript at a later point in the page life?

Basically I need to know if it's safe to use this code, when I know for sure certain machines won't be able to make sense of it.

My code is structured like this:

  2. <script type="text/javascript">
  3.     
  4.         var t = performance.timing;
  5.         var kbytes;
  6.         var networkLatency;
  7.         var browserRenderTime;
  8.         var totalTime;

  10.         // Gets hit 1st
  11.         $(document).ready(
  12.             function () {
  13.                 var pagebytes = $('html').html().length;
  14.                 kbytes = pagebytes / 1024;
  15.                 $('#Div4').text('Page Size = ' + kbytes.toFixed(0) + 'Kb');
  16.             }
  17.         );

  19.         // Gets hit 2nd
  20.         var startTime = new Date().getTime();
  21.         function onLoadEventHandler() {
  22.             networkLatency = t.responseEnd - t.fetchStart;
  23.             $('#Div1').text('Network latency = ' + networkLatency + 'ms');
  24.         }

  26.         // Gets hit 3rd
  27.         $(window).load(function () {
  28.             setTimeout(function () {
  29.                 browserRenderTime = t.loadEventEnd - t.responseEnd;
  30.                 totalTime = t.loadEventEnd - t.navigationStart;
  31.                 $('#Div2').text('The time taken for client machine to render page = ' + browserRenderTime + 'ms');
  32.                 $('#Div3').text('The whole process = ' + totalTime + 'ms');

  34.                 var data = kbytes.toFixed(0);
  35.                 data += "|" + $('#DivServerExecutionTime').text();
  36.                 data += "|" +  networkLatency;
  37.                 data += "|" +  browserRenderTime;
  38.                 data += "|" + totalTime;
  39.                 data += "|" + (screen.width + " x " + screen.height);
  40.                 data += "|" + window.location;

  42.                 $.ajax({
  43.                     type: 'POST',
  44.                     url: "/handlers/PageloadSpeeds.ashx",
  45.                     cache: false,
  46.                     data: data
  47.                 });

  49.             }, 0);
  50.         });

  52.     </script>