deconstructing errorception's snippet

errorception-deconstructed.js

// Original snippet:
// https://errorception.com/docs

var SCRIPT_EL = 'script';

function (window, document, SCRIPT_EL, PROJ_ID) {
	// Set a global variable called '_errs' to an array with our PROJ_ID in it
	window._errs = [PROJ_ID];
	
	// Specify our method to be executed when 'onerror' fires. This gives us
	// the ability to grab the arguments passed to onerror, stash them, and 
	// then call onerror as usual.
	var myOnErrMethod = window.onerror;
	window.onerror = function() {
		// Reference the special 'arguments' param available in every JS func
		var args = arguments;
		// Add what's in 'arguments' to our error array
		_errs.push(args);
		// If myOnErrMethod exists (doesn't return null), run it in 'this'
		// context, giving onError the arguments it was originally passed.
		myOnErrMethod && myOnErrMethod.apply(this, args);
	};
	
	// Add the reference to our tracking script as a <script> element before 
	// the first <script> already in the page. 
	var createErrReporterElement = function() {
		var scriptEl = document.createElement(SCRIPT_EL);
		var firstScriptInPage = document.getElementsByTagName(SCRIPT_EL)[0];
		scriptEl.src = "//beacon.errorception.com/" + PROJ_ID + ".js";
		scriptEl.async = !0;
		firstScriptInPage.parentNode.insertBefore(scriptEl, firstScriptInPage);
	};
	
	// Depending on whether 'addEventListener' is present (i.e., whether we're
	// in old IE or not), use the appropriate method to attach our function
	// to the 'onload' event.
	window.addEventListener ? window.addEventListener("load", createErrReporterElement, !1) : window.attachEvent("onload", createErrReporterElement)
};