Pure js dom ready

purejs_domready.js

(function(funcName, baseObj) {
  // The public function name defaults to window.docReady
  // but you can pass in your own object and own function name and those will be used
  // if you want to put them in a different namespace
  funcName = funcName || "docReady";
  baseObj = baseObj || window;
  var readyList = [];
  var readyFired = false;
  var readyEventHandlersInstalled = false;

  // call this when the document is ready
  // this function protects itself against being called more than once
  function ready() {
    if (!readyFired) {
      // this must be set to true before we start calling callbacks
      readyFired = true;
      for (var i = 0; i < readyList.length; i++) {
        // if a callback here happens to add new ready handlers,
        // the docReady() function will see that it already fired
        // and will schedule the callback to run right after
        // this event loop finishes so all handlers will still execute
        // in order and no new ones will be added to the readyList
        // while we are processing the list
        readyList[i].fn.call(window, readyList[i].ctx);
      }
      // allow any closures held by these functions to free
      readyList = [];
    }
  }

  function readyStateChange() {
    if ( document.readyState === "complete" ) {
      ready();
    }
  }

  // This is the one public interface
  // docReady(fn, context);
  // the context argument is optional - if present, it will be passed
  // as an argument to the callback
  baseObj[funcName] = function(callback, context) {
    if (typeof callback !== "function") {
      throw new TypeError("callback for docReady(fn) must be a function");
    }
    // if ready has already fired, then just schedule the callback
    // to fire asynchronously, but right away
    if (readyFired) {
      setTimeout(function() {callback(context);}, 1);
      return;
    } else {
      // add the function and context to the list
      readyList.push({fn: callback, ctx: context});
    }
    // if document already ready to go, schedule the ready function to run
    if (document.readyState === "complete") {
      setTimeout(ready, 1);
    } else if (!readyEventHandlersInstalled) {
      // otherwise if we don't have event handlers installed, install them
      if (document.addEventListener) {
        // first choice is DOMContentLoaded event
        document.addEventListener("DOMContentLoaded", ready, false);
        // backup is window load event
        window.addEventListener("load", ready, false);
      } else {
        // must be IE
        document.attachEvent("onreadystatechange", readyStateChange);
        window.attachEvent("onload", ready);
      }
      readyEventHandlersInstalled = true;
    }
  }
})("docReady", window);