Develop Reference

Unload a Javascript from memory

I am thinking of a web application on browsers. I can dynamically add required js files as needed while traversing through different parts of application, but can I unload unnecessary js content from the current session's "memory" as the memory usage grows over time?
I know it is possible to remove the tag responsible for the content but it is not assured that it will eventually unload and unbind everything correspondent to that content.
Thanks

I know it is possible to remove the tag responsible for the content but it is not assured that it will eventually unload and unbind everything correspondent to that content.
In fact, it's assured that it will not. Once the JavaScript is loaded and executed, there is no link between it and the script element that loaded it at all.
You can dynamically load and unload modules, but you have to design it into your code by
Having a module have a single symbol that refers to the module as a whole
Having an "unload" function or similar that is responsible for removing all of a module's event listeners and such
Then unloading the module is a matter of calling its unload function and then setting the symbol that refers to it to undefined (or removing it entirely, if it's a property on an object).
Here's a very simple demonstration of concept (which you'd adapt if you were using some kind of Asynchronous Module Definition library):
// An app-wide object containing a property for each module.
// Each module can redefine it in this way without disturbing other modules.
var AppModules = AppModules || {};
// The module adds itself
AppModules.ThisModule = (function() {
var unloadCallbacks = [];
function doThis() {
// Perhaps it involves setting up an event handler
var element = document.querySelector(/*...*/);
element.addEventHandler("click", handler, false);
unloadCallbacks.push(function() {
element.removeEventHandler("click", handler, false);
element = handler = undefined;
});
function handler(e) {
// ...
}
}
function doThat() {
// ...
}
function unload() {
// Handle unloading any handlers, etc.
var callbacks = unloadCallbacks;
unloadCallbacks = undefined;
callbacks.forEach(function(callback) {
callback();
});
// Remove this module
delete AppModules.ThisModule;
}
return {
doThis: doThis,
unload: unload
};
})();
That callbacks mechanism is very crude, you'd want something better. But it demonstrates the concept.

Script not loaded directly

I'm loading a HTML partial through ajax. The partial is attached to the DOM by using innerHTML on an existing node.
The partial contains a few script tags at the bottom, something like:
<script src="/Scripts/Griffin.Editor.js" type="text/javascript"></script>
<script type="text/javascript">
marked.setOptions({
renderer: new marked.Renderer(),
gfm: true,
tables: true,
breaks: false,
pedantic: false,
sanitize: true,
smartLists: true,
smartypants: false
});
var textParser = {
parse: function (text) {
return marked(text);
}
}
var prismHighlighter = {
highlight: function (blockElements, inlineElements) {
blockElements.forEach(function(item) {
Prism.highlightElement(item);
});
}
};
var editor = new Griffin.Editor('editor', textParser);
editor.syntaxHighlighter = prismHighlighter;
editor.preview();
</script>
However, as the script tags are not executed, I traverse the loaded partial to identify all script tags. I then create new script nodes in the DOM and attach them to the HEAD.
Something like:
var scripts = viewElem.getElementsByTagName('script');
for (let i = 0; i < len; i++) {
var scriptTag = scripts[0];
let node = document.createElement('script');
if (scriptTag.src && scriptTag.src.length > 0) {
node.src = scriptTag.src;
node.type = scriptTag.type;
} else {
node.text = scriptTag.text;
node.type = scriptTag.type;
//had eval here before (instead of attaching the embedded script to the HEAD).
}
document.head.appendChild(node);
scriptTag.parentNode.remove(scriptTag);
}
From what I understand the browser should load the referenced scripts before invoking the embedded script. That is however not the case for me, because the JS console complains about not finding the object defined in the dependency script.
If I use a timer and eval the embedded script in it everything works. But that seems as a ugly workaround and I really want to understand the mechanics behind the load behavior (i.e. why the scripts are not executed when the partial is attached to the DOM and why the referenced scripts are not loaded directly when I add the nodes to the HEAD tag).

From what I've encountered, you can't have immediately executing JavaScript inside an Ajax response. The reason being you are trying to execute JavaScript inside another JavaScript function. So the browser has no idea which executing context to use with this scenario.
I would recommend using deferred execution like you mentioned. Except, you need to let the browser interpret the Ajax response first. For example:
$.get('url', function (html) {
// html = "<script>function myTest () { console.log('here'); }</script>"
$('#result').html(html);
// Now that the DOM has had time to parse the response we can do:
myTest();
});
Notice it is the Ajax callback invoking the response function not the response immediately executing itself. Hope this helps.

I found a really great article explaining in depth how scripts are loaded into the browser.
In essence you can't be sure of execution order per default when you include scripts dynamically. To be sure of the order you need to do one of the following
a. Use async=false if supported
b. Use readyState (for ie<10)
c. Use defer attribute.
Try to use the mentioned features in that order to be sure.
However, even if you do all that you will still get screwed if you mix embedded scripts (code in in the script tag) with referenced scripts (using src attribute).
The problem is that the embedded scripts will run directly, even if the references script tags are added before. To solve that you need to push the embedded scripts into a queue and hook the load event for all referenced scripts.
Once all referenced scripts have toggled the load even you are free to invoke the embedded scripts (either by added the script tags to an element or by eval their text property).
Source: http://blog.gauffin.org/2015/07/embedded-script-tags-in-content-loaded-through-ajax-and-execute-the-script-tags-dynamically/

Does an Event fire when adding a property to the window element?

When loading JavaScript libraries (like jQuery), they tend to create an object on the Window element.
I'm trying to work out how I can detect when the library has just loaded so I've gone down the path of trying to detect a property change on the window object...
window.addEventListener("DOMAttrModified", invalidate, false);
function invalidate(evt)
{
console.log('attrChange = ' + evt.attrChange);
}
... This doesn't work.
Perhaps someone knows of another way to solve both this solution and a mechanism to detect when an external library has loaded.
p.s. I have looked at the onload tag for the script tag but I'm concerned as it's not in the W3C.
p.p.s. Ultimately, I'm trying to implement a function where it is safe to use jQuery code.

If your js code is lower then script tag then don't worry, html rendering stops while script tag is not loaded, so if your js is lower then library is already loaded.
Also you may check for existence of some variable (like $).
if (typeof jQuery != 'undefined') {
// is loaded
} else {
// is not loaded
}
Or in loop though interval:
var interval = setInterval(function () {
if (typeof jQuery != 'undefined') {
clearInterval(interval);
// do what you want
}
});

How to determine if CKEditor is loaded?

How do I find out if CKEditor is loaded? I've looked through the API docs, but could only find the loaded event. I want to check if CKEditor is loaded, because if I load it a second time, my textareas disapears.

The loaded event didn't work for me. instanceReady worked:
CKEDitor_loaded = false;
CKEDITOR.on('instanceReady', function(){ CKEditor_loaded = true; });

var waitCKEDITOR = setInterval(function() {
if (window.CKEDITOR) {
clearInterval(waitCKEDITOR);
//CKEDITOR.replace(...);
}
}, 100/*milli*/);

I've looked through the API docs, but could only find the loaded event.
I don't know whether there exists a specific property for this - there might! - but you could use the loaded event to set a global flag. It's not really nice but would do the job.
// At the top of the script
CKEDitor_loaded = false;
// then later
CKEDITOR.on('loaded', function(){ CKEditor_loaded = true; });
Instead of a global variable, you could also consider setting something inside CKEDITOR:
CKEDITOR.flag_loaded = true;
This would be a bit cleaner.

If instance is not ready, the text set would be discarded
On initialization of the CkEditor (version 4 here), you should never set any data before the editor is ready to handle it.
// Initialize this._editor with replace
if (this._editor.status !== "ready") {
this._editor.on("instanceReady",
event => {
event.editor.setData(data);
});
} else {
this._editor.setData(data);
}

Hope this helps someone.
I also load a page snippet with CKEDITOR functionality via AJAX and as such I have experienced many of the problems outlined in this question. This is my solution:
function setCk(id){
if(window.CKEDITOR){
var _instId = CKEDITOR.instances[id];
if(_instId == undefined){
CKEDITOR.inline(id);
}else{
CKEDITOR.instances[id].destroy();
CKEDITOR.inline(id);
}
}
}
On each AJAX response for this snippet I inject a script element into the head with a call to setCk(textareaId). The trick being to destroy any previous CKEDITOR instances for the target ID & re-initialise CKEDITOR after each AJAX snippet load.

I know this is a very old post, but in my research it kept coming up. I am dynamically loading the CKEditor through jQuery. I didn't want to load it multiple times since things start happening, as you found out.
Simple solution:
if (!window.CKEDITOR) {
// (not loaded yet, your code to load it)
}

//creating instance of ck-editor
var yourInstance = CKEDITOR.instances.yourContainer;
//check instance of your ck-editor
if(yourInstance){
//destroy instance
yourInstance .destroy(true);
}
// create instance again
CKEDITOR.replace( 'yourContainer' );

CKEditor instance already exists

I am using jquery dialogs to present forms (fetched via AJAX). On some forms I am using a CKEditor for the textareas. The editor displays fine on the first load.
When the user cancels the dialog, I am removing the contents so that they are loaded fresh on a later request. The issue is, once the dialog is reloaded, the CKEditor claims the editor already exists.
uncaught exception: [CKEDITOR.editor] The instance "textarea_name" already exists.
The API includes a method for destroying existing editors, and I have seen people claiming this is a solution:
if (CKEDITOR.instances['textarea_name']) {
CKEDITOR.instances['textarea_name'].destroy();
}
CKEDITOR.replace('textarea_name');
This is not working for me, as I receive a new error instead:
TypeError: Result of expression 'i.contentWindow' [null] is not an object.
This error seems to occur on the "destroy()" rather than the "replace()". Has anyone experienced this and found a different solution?
Is is possible to 're-render' the existing editor, rather than destroying and replacing it?
UPDATED
Here is another question dealing with the same problem, but he has provided a downloadable test case.

For this to work you need to pass boolean parameter true when destroying instance:
var editor = CKEDITOR.instances[name];
if (editor) { editor.destroy(true); }
CKEDITOR.replace(name);

function loadEditor(id)
{
var instance = CKEDITOR.instances[id];
if(instance)
{
CKEDITOR.remove(instance);
}
CKEDITOR.replace(id);
}

I had this problem too, but I solved it in a much simpler way...
I was using the class "ckeditor" in my jQuery script as the selector for which textareas I wanted use for CKEditor. The default ckeditor JS script also uses this class to identify which textareas to use for CKEditor.
This meant there is a conflict between my jQuery script and the default ckeditor script.
I simply changed the class of the textarea and my jQuery script to 'do_ckeditor'(you could use anything except "ckeditor") and it worked.

This is the simplest (and only) solution that worked for me:
if(CKEDITOR.instances[editorName])
delete CKEDITOR.instances[editorName];
CKEDITOR.replace(editorName);
Deleting this entry in the array prevents this form safety check from destroying your application.
destroy() and remove() did not work for me.

Perhaps this will help you out - I've done something similar using jquery, except I'm loading up an unknown number of ckeditor objects. It took my a while to stumble onto this - it's not clear in the documentation.
function loadEditors() {
var $editors = $("textarea.ckeditor");
if ($editors.length) {
$editors.each(function() {
var editorID = $(this).attr("id");
var instance = CKEDITOR.instances[editorID];
if (instance) { instance.destroy(true); }
CKEDITOR.replace(editorID);
});
}
}
And here is what I run to get the content from the editors:
var $editors = $("textarea.ckeditor");
if ($editors.length) {
$editors.each(function() {
var instance = CKEDITOR.instances[$(this).attr("id")];
if (instance) { $(this).val(instance.getData()); }
});
}
UPDATE: I've changed my answer to use the correct method - which is .destroy(). .remove() is meant to be internal, and was improperly documented at one point.

var e= CKEDITOR.instances['sample'];
e.destroy();
e= null;

I've had similar issue where we were making several instances of CKeditor for the content loaded via ajax.
CKEDITOR.remove()
Kept the DOM in the memory and didn't remove all the bindings.
CKEDITOR.instance[instance_id].destroy()
Gave the error i.contentWindow error whenever I create new instance with new data from ajax. But this was only until I figured out that I was destroying the instance after clearing the DOM.
Use destroy() while the instance & it's DOM is present on the page, then it works perfectly fine.

For ajax requests,
for(k in CKEDITOR.instances){
var instance = CKEDITOR.instances[k];
instance.destroy()
}
CKEDITOR.replaceAll();
this snipped removes all instances from document.
Then creates new instances.

The i.contentWindow is null error seems to occur when calling destroy on an editor instance that was tied to a textarea no longer in the DOM.
CKEDITORY.destroy takes a parameter noUpdate.
The APIdoc states:
If the instance is replacing a DOM element, this parameter indicates whether or not to update the element with the instance contents.
So, to avoid the error, either call destroy before removing the textarea element from the DOM, or call destory(true) to avoid trying to update the non-existent DOM element.
if (CKEDITOR.instances['textarea_name']) {
CKEDITOR.instances['textarea_name'].destroy(true);
}
(using version 3.6.2 with jQuery adapter)

This is what worked for me:
for(name in CKEDITOR.instances)
{
CKEDITOR.instances[name].destroy()
}

CKEDITOR.instances = new Array();
I am using this before my calls to create an instance (ones per page load). Not sure how this affects memory handling and what not. This would only work if you wanted to replace all of the instances on a page.

I've prepared my own solution based on all above codes.
$("textarea.ckeditor")
.each(function () {
var editorId = $(this).attr("id");
try {
var instance = CKEDITOR.instances[editorId];
if (instance) { instance.destroy(true); }
}
catch(e) {}
finally {
CKEDITOR.replace(editorId);
}
});
It works perfectly for me.
Sometimes after AJAX request there is wrong DOM structure.
For instace:
<div id="result">
<div id="result>
//CONTENT
</div>
</div>
This will cause issue as well, and ckEditor will not work. So make sure that you have correct DOM structure.

i had the same problem with instances, i was looking everywhere and finally this implementation works for me:
//set my instance id on a variable
myinstance = CKEDITOR.instances['info'];
//check if my instance already exist
if (myinstance) {
CKEDITOR.remove(info)
}
//call ckeditor again
$('#info').ckeditor({
toolbar: 'Basic',
entities: false,
basicEntities: false
});

You can remove any ckeditor instance by remove method of ckeditor. Instance will be id or name of the textarea.
if (CKEDITOR.instances[instance_name]) {
CKEDITOR.remove(CKEDITOR.instances[instance_name]);
}

Indeed, removing the ".ckeditor" class from your code solves the issue. Most of us followed the jQuery integration example from the ckeditor's documentation:
$('.jquery_ckeditor')
.ckeditor( function() { /* callback code */ }, { skin : 'office2003' } );
and thought "... maybe I can just get rid or the '.jquery_' part".
I've been wasting my time tweaking the callback function (because the {skin:'office2003'} actually worked), while the problem was coming from elsewhere.
I think the documentation should mention that the use of "ckeditor" as a class name is not recommended, because it is a reserved keyword.
Cheers.

I learned that
delete CKEDITOR.instances[editorName];
by itself, actually removed the instance. ALL other methods i have read and seen, including what was found here at stackoverflow from its users, did not work for me.
In my situation, im using an ajax call to pull a copy of the content wrapped around the and 's. The problem happens to be because i am using a jQuery .live event to bind a "Edit this document" link and then applying the ckeditor instance after success of the ajax load. This means, that when i click another link a link with another .live event, i must use the delete CKEDITOR.instances[editorName] as part of my task of clearing the content window (holding the form), then re-fetching content held in the database or other resource.

I hade the same problem with a jQuery Dialog.
Why destroy the instance if you just want to remove previous data ?
function clearEditor(id)
{
var instance = CKEDITOR.instances[id];
if(instance)
{
instance.setData( '' );
}
}

I chose to rename all instances instead of destroy/replace - since sometimes the AJAX loaded instance doesn't really replace the one on the core of the page... keeps more in RAM, but less conflict this way.
if (CKEDITOR && CKEDITOR.instances) {
for (var oldName in CKEDITOR.instances) {
var newName = "ajax"+oldName;
CKEDITOR.instances[newName] = CKEDITOR.instances[oldName];
CKEDITOR.instances[newName].name = newName;
delete CKEDITOR.instances[oldName];
}
}

I am in the situation where I have to controls that spawn dialogs, each of them need to have a ckeditor embedded inside these dialogs. And it just so happens the text areas share the same id. (normally this is very bad practice, but I have 2 jqGrids, one of assigned items and another of unassigned items.) They share almost identical configuration. Thus, I am using common code to configure both.
So, when I load a dialog, for adding rows, or for editing them, from either jqGrid; I must remove all instances of CKEDITOR in all textareas.
$('textarea').each(function()
{
try
{
if(CKEDITOR.instances[$(this)[0].id] != null)
{
CKEDITOR.instances[$(this)[0].id].destroy();
}
}
catch(e)
{
}
});
This will loop over all textareas, and if there is a CKEDITOR instance, then destroy it.
Alternatively if you use pure jQuery:
$('textarea').each(function()
{
try
{
$(this).ckeditorGet().destroy();
}
catch(e)
{
}
});

remove class="ckeditor" , it might have triggered ckeditor initialization

I had the same problem where I was receiving a null reference exception and the word "null" would be displayed in the editor. I tried a handful of solutions, including upgrading the editor to 3.4.1 to no avail.
I ended up having to edit the source. At about line 416 to 426 in _source\plugins\wysiwygarea\plugin.js, there's a snippet like this:
iframe = CKEDITOR.dom.element.createFromHtml( '<iframe' + ... + '></iframe>' );
In FF at least, the iframe isn't completely instantiated by the time it's needed. I surrounded the rest of the function after that line with a setTimeout function:
iframe = CKEDITOR.dom.element.createFromHtml( '<iframe' + ... + '></iframe>' );
setTimeout(function()
{
// Running inside of Firefox chrome the load event doesn't bubble like in a normal page (#5689)
...
}, 1000);
};
// The script that launches the bootstrap logic on 'domReady', so the document
...
The text renders consistently now in the modal dialogs.

To support dynamic (Ajax) loading of forms (without page refreshes between) which contain textareas with the same (same form is called again) or different ID's (previously unloaded form) and convert them to CKEditor elements I did the following (using the JQuery adapter):
After the page has finished every Ajax call that delivers a textarea to be converted, I make a call to the following function:
setupCKeditor()
This looks like this (it assumes your textareas to be converted to RTE's have class="yourCKClass"):
/* Turns textAreas into TinyMCE Rich Text Editors where
* class: tinymce applied to textarea.
*/
function setupCKeditor(){
// define editor configuration
var config = {skin : 'kama'};
// Remove and recreate any existing CKEditor instances
var count = 0;
if (CKEDITOR.instances !== 'undefined') {
for(var i in CKEDITOR.instances) {
var oEditor = CKEDITOR.instances[i];
var editorName = oEditor.name;
// Get the editor data.
var data = $('#'+editorName).val();
// Check if current instance in loop is the same as the textarea on current page
if ($('textarea.yourCKClass').attr('id') == editorName) {
if(CKEDITOR.instances[editorName]) {
// delete and recreate the editor
delete CKEDITOR.instances[editorName];
$('#'+editorName).ckeditor(function() { },config);
count++;
}
}
}
}
// If no editor's exist in the DOM, create any that are needed.
if (count == 0){
$('textarea.yourCKClass').each( function(index) {
var editorName = $(this).attr('id');
$('#'+editorName).ckeditor(function() { $('#'+editorName).val(data); },config);
});
}
}
I should mention that the line:
$('#'+editorName).ckeditor(function() { $('#'+editorName).val(data); },config);
could (and should) be simply:
$('#'+editorName).ckeditor(function() { },config);
however I found that the editor would often show the correct content for a second after loading and them empty the editor of the desired content. So that line with the callback code forces the CKEditor content to be the same as the originating textarea content. Causes a flicker when used. If you can avoid using it, do so..

I had exactly the same problem like jackboberg. I was using dynamic form loading into jquery dialogs then attaching various widgets (datepickers, ckeditors etc...).
And I tried all solutions noted above, none of them worked for me.
For some reason ckeditor only attached the first time I loaded form, the second time I got exactly the same error message jackboberg did.
I've analyzed my code and discovered that if you attach ckeditor in "mid-air" that is while form content is still not placed into dialog, ckeditor won't properly attach its bindings. That is since ckeditor is attached in "mid-air", second time you attach it in "mid-air"... poof ... an error is thrown since the first instance was not properly removed from DOM.
This was my code that ptoduced the error:
var $content = $(r.content); // jQuery can create DOM nodes from html text gotten from <xhr response> - so called "mid-air" DOM creation
$('.rte-field',$content).ckeditor(function(){});
$content.dialog();
This is the fix that worked:
var $content = $(r.content).dialog(); // first create dialog
$('.rte-field',$content).ckeditor(function(){}); // then attach ckeditor widget

I ran into this exact same thing and the problem was that the wordcount plugin was taking too long to initialize. 30+ seconds. The user would click into the view displaying the ckeditor, then cancel, thereby ajax-loading a new page into the dom. The plugin was complaining because the iframe or whatever contentWindow is pointing to was no longer visible by the time it was ready to add itself to the contentWindow. You can verify this by clicking into your view and then waiting for the Word Count to appear in the bottom right of the editor. If you cancel now, you won't have a problem. If you don't wait for it, you'll get the i.contentWindow is null error. To fix it, just scrap the plugin:
if (CKEDITOR.instances['textarea_name'])
{
CKEDITOR.instances['textarea_name'].destroy();
}
CKEDITOR.replace('textarea_name', { removePlugins: "wordcount" } );
If you need a word counter, register for the paste and keyup events on the editor with a function that counts the words.

For those using the jquery "adapter" and having trouble (as I was), as super hackish yet working solution is to do something like this:
// content editor plugin
(function($){
$.fn.contentEditor = function( params ) {
var xParams = $.extend({}, $.fn.contentEditor.defaultParams, params);
return this.each( function() {
var $editor = $(this);
var $params = $.extend({}, xParams, $editor.data());
// if identifier is set, detect type based on identifier in $editor
if( $params.identifier.type ) {
$params.type = $editor.find($params.identifier.type).val();
}
$editor.data('type', $params.type);
// edit functionality
editButton = $('<button>Edit Content</button>').on('click',function(){
// content container
var $cc = $('#' + $editor.data('type'));
// editor window
var $ew = $('<form class="editorWindow" />');
$ew.appendTo('body');
// editor content
$ec = $('<textarea name="editorContent" />').val($cc.html());
$ec.appendTo($ew);
$ec.ckeditor();
//$ec.ckeditorGet().setMode('source');
$ew.dialog({
"autoOpen": true,
"modal": true,
"draggable": false,
"resizable": false,
"width": 850,
"height": 'auto',
"title": "Content Editor",
"buttons": {
'Save': function() {
$cc.html( $ec.val() );
$ec.ckeditorGet().destroy();
$ew.remove();
},
'Cancel / Close': function() {
$ec.ckeditorGet().destroy();
$ew.remove();
}
},
'close': function() {
$ec.ckeditorGet().destroy();
},
'open': function() {
$ew.find('a.cke_button_source').click();
setTimeout(function(){
$ew.find('a.cke_button_source.cke_on').click();
}, 500);
}
});
return false;
});
editButton.appendTo( $editor );
});
}
// set default option values
$.fn.contentEditor.defaultParams = {
'identifier': {
'type': 'input[name="type"]'
}
};
})(jQuery);
$(function(){
$('form.contentEditor').contentEditor();
});
The key point being this part:
'open': function() {
$ew.find('a.cke_button_source').click();
setTimeout(function(){
$ew.find('a.cke_button_source.cke_on').click();
}, 500);
}
This fixes the problem with the editor text not being visible the next time you open the dialog. I realise this is very hackish, but considering that most of these are going to be used for admin tools, I don't think that's as big a concern as it normally would be.. and this works, so hopefully it will save someone some time ;)

This is the fully working code for jquery .load() api and ckeditor, in my case I am loading a page with ckeditor into div with some jquery effects. I hope it will help you.
$(function() {
runEffect = function(fileload,lessonid,act) {
var selectedEffect = 'drop';
var options = {};
$( "#effect" ).effect( selectedEffect, options, 200, callback(fileload,lessonid,act) );
};
function callback(fileload,lessonid,act) {
setTimeout(function() {//load the page in effect div
$( "#effect" ).load(fileload,{lessonid:lessonid,act:act});
$("#effect").show( "drop",
{direction: "right"}, 200 );
$("#effect").ajaxComplete(function(event, XMLHttpRequest, ajaxOptions) {
loadCKeditor(); //call the function after loading page
});
}, 100 );
};
function loadCKeditor()
{//you need to destroy the instance if already exist
if (CKEDITOR.instances['introduction'])
{
CKEDITOR.instances['introduction'].destroy();
}
CKEDITOR.replace('introduction').getSelection().getSelectedText();
}
});
===================== button for call the function ================================
<input type="button" name="button" id="button" onclick="runEffect('lesson.php','','add')" >

Its pretty simple. In my case, I ran the below jquery method that will destroy ckeditor instances during a page load. This did the trick and resolved the issue -
JQuery method -
function resetCkEditorsOnLoad(){
for(var i in CKEDITOR.instances) {
editor = CKEDITOR.instances[i];
editor.destroy();
editor = null;
}
}
$(function() {
$(".form-button").button();
$(".button").button();
resetCkEditorsOnLoad(); // CALLING THE METHOD DURING THE PAGE LOAD
.... blah.. blah.. blah.... // REST OF YOUR BUSINESS LOGIC GOES HERE
});
That's it. I hope it helps you.
Cheers,
Sirish.

This functions works for me in CKEditor version 4.4.5, it does not have any memory leaks
function CKEditor_Render(CkEditor_id) {
var instance = CKEDITOR.instances[CkEditor_id];
if (CKEDITOR.instances.instance) {
CKEDITOR.instances.instance.destroy();
}
CKEDITOR.replace(CkEditor_id);
}
// call this function as below
var id = 'ckeditor'; // Id of your textarea
CKEditor_Render(id);

CKeditor 4.2.1
There is a lot of answers here but for me I needed something more (bit dirty too so if anyone can improve please do). For me MODALs where my issue.
I was rendering the CKEditor in a modal, using Foundation. Ideally I would have destoryed the editor upon closing, however I didn't want to mess with Foundation.
I called delete, I tried remove and another method but this was what I finally settled with.
I was using textarea's to populate not DIVs.
My Solution
//hard code the DIV removal (due to duplication of CKeditors on page however they didn't work)
$("#cke_myckeditorname").remove();
if (CKEDITOR.instances['myckeditorname']) {
delete CKEDITOR.instances['myckeditorname'];
CKEDITOR.replace('myckeditorname', GetCKEditorSettings());
} else {
CKEDITOR.replace('myckeditorname', GetCKEditorSettings());
}
this was my method to return my specific formatting, which you might not want.
function GetCKEditorSettings()
{
return {
linkShowAdvancedTab: false,
linkShowTargetTab: false,
removePlugins: 'elementspath,magicline',
extraAllowedContent: 'hr blockquote div',
fontSize_sizes: 'small/8px;normal/12px;large/16px;larger/24px;huge/36px;',
toolbar: [
['FontSize'],
['Bold', 'Italic', 'Underline', '-', 'NumberedList', 'BulletedList', '-', 'Link', 'Unlink'],
['Smiley']
]
};
}

Try this:
for (name in CKEDITOR.instances)
{
CKEDITOR.instances[name].destroy(true);
}