Get all javascript errors on page/javascript error handling
<p>I want to be able to send myself all the javascript errors on a page. I am an extension developer, so the following has an emphasis on making sure the dom is ready before making calls to it. </p>

<p>I investigated adding some functionality to the <code>throw</code> to also send or mail the exceptions, but I didn't find this to be possible.</p>

<p>1:main solution to this, a <em>window.onerror handler</em>:</p>

<pre><code>window.onerror = function(e, url, line){
  mailError('onerror: ' + e + ' URL:' + url + ' Line:' + line);
  console.error('\nLine ' + line + ':');
  setTimeout(function(){retry();}, 100); //mainly useful in content scripts for extensions, 
  return true; 
}
</code></pre>

<p>May also need to do same thing via jQuery:</p>

<pre><code>$(window).error( 
  function(e, url, line){
    //handle error
  }
);
</code></pre>

<p>The downfall of this is that your code has stopped executing. </p>

<p>To avoid errors stopping execution, it's best to use callbacks to make sure code executes in a certain sequence, and to utilize events wherever possible. You can also protect dom calls with a few techniques</p>

<pre><code>$(document).ready({
  //you usually won't get bad dom calls wrapping your code in this
});
</code></pre>

<p>You can also consider running code on window.onload</p>

<pre><code>window.onload = function(){
  //you page will probably twitch upon executing code at this time
  //but you will almost never have a bad dom call
};
</code></pre>

<p>Another technique</p>

<pre><code>if (document.getElementById('iNeedThisElement')) {
  //doin work!
  document.getElementById('iNeedThisElement').style.display = 'block';
} else {
  var stillNeedToTakeCareOfX = true; //false otherwise since it's undefined
  mailError('iNeedThisElement was unavailable...');
}
</code></pre>

<p>Using these techniques and just debugging your application, you should be fairly well off. Since console.error, .warn, and .log statements cannot be retrieved and reported back to your, a small alternative suite is provided below:</p>

<pre><code>var Xe = { }; //Extreme error suite

function extraInfo(e){
   //e optional
   if(!e)e = true;

   //add an extra debug info, such as navigator or current URL
   return ' currentURL: '+ document.URL + 
        '\n userAgent: ' + navigator.userAgent + 
        '\n platform: '  + navigator.platform + 
        '\n userid: '    + localStorage.userid + 
        '\n language: '  + navigator.langauge + 
        '\n cookies?: '  + navigator.cookiesEnabled;
}

Xe.error = function(e){
  console.error(e); //maintain original functionality
  mailError('Xe err: ' + e + extraInfo() );
}


Xe.warn = function(e){
  console.warn(e);
  mailError('Xe warn: ' + e + extraInfo() );
}


Xe.log = function(e){
  console.log(e);
  mailError('Xe log: ' + e + extraInfo() );
}
</code></pre>

<p>As a last ditch, you can continually attempt to execute a chunk of code until it executes without errors. This is "2" below.</p>

<p>2:group code in large chunks and attempting to re-execute x seconds later after catching an error, or continue to next chunk of code</p>

<pre><code>//defExe = DEFinitely EXEcute this code
  //functionArg, reference to a function holding a large chunk of code
  //seconds, timeout in milliseconds to re-attempt error free execution of this function
function defExe(functionArg, seconds) {
  //seconds is optional
  if (!seconds)seconds = 300;

  try {
    functionArg();
  } catch(e) {
    //mail the error plus extra info
    mailError('caught ' + e + ' attempting to re-execute ' + functionArg.name + ' in ' + seconds + ' milliseconds');

    //re-attempt to execute this code
    setTimeout(function(){ 
       defExe(functionArg, seconds); 
    }, seconds);
  }
}
</code></pre>

<p>this it is then used like</p>

<pre><code>//array to group function chunks
var fn = [ ];

fn[1] = function (){
  //a large chunk of javascript
}
defExe(fn[1]);

fn[2] = function(){
  //another chunk of your program
}
defExe(fn[2]);
</code></pre>

<p>#2 Summary: Group code in functions and run in try-catch block, repeating if an errors are caught</p>
