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Use both $ and jquery as variable

In my project every page loads a cdn jquery script. some use $ and some use jquery. and now I have to use my new script file 'myNewScript.js' in every page.
If I write my function like $(function (){}) it gives error on some pages like
$ is not function
and if I write function like this jquery(function (){}) then it also give error on other page like
jquery is not a function.
I want to know can we use both $ and jquery as variable . like in same script file say 'myNewScript.js' I want to write $(function (){}) and jquery(function (){}).
Every thing is dependent on each other so I can't reverse the loading of the script. I can't think of any solution...

jQuery should always be available using the name jQuery (note the uppercase Q). So use that:
jQuery(function (){})
You can also wrap your code in an IIFE if you would like to refer to jQuery as $ while dealing with the uncertainty whether the global $ actually refers to it:
(function ($) {
$(function () {
// on ready stuff
});
})(jQuery);

Define jQuery locally for yourself by looking for both variables.
var myJquery = jquery || $;

JavaScript WordPress uncaught typeerror $ is not a function

$(document).ready(function(){
$(".showhide").click(function(){
$("nav").slideToggle("slow");
});
});
I'm not a JavaScript programmer. I'm getting this error: Uncaught TypeError $ is not a function
For some reason my navigation is not working.
Someone told me to put this in JavaScript but I'm getting the error.
Found this: jQuery(document); but don't know how to use this.

This is how you should do it specially on WordPress (since Wordpress is usually using jQuery instead of $)
(function($){
$(document).ready(function(){
$(".showhide").click(function(){
$("nav").slideToggle("slow");
});
});
})(jQuery);
Reference here
or if you don't like the answer above, you can add var $ = jQuery; before the $(document).ready function

The issue is that WordPress uses jQuery in compatibility mode, which means that it does NOT utilize the $ by default.
You CAN use the $ to access jQuery, but you just need to wrap it in a document ready function.
Here's the simplest way to do this:
// By passing the $ as a function argument, $ is available anywhere inside this document ready function
jQuery(function($) {
// Do all your $ jQuery goodness in here...
$(".showhide").click(function(){
$("nav").slideToggle("slow");
});
// $ is available until the end of the document ready
});
// Outside of the document ready function - now you cannot use $ - you'd have to use jQuery....
jQuery('.showhide').click(....);
For completeness sake, be sure you have enqueued jQuery.
In your theme's functions.php file, or in your plugin's main file, add this:
function theme_name_scripts() {
wp_enqueue_script( 'jquery' );
}
add_action( 'wp_enqueue_scripts', 'theme_name_scripts' );
This ensures that jQuery is loaded - the right way - in your WordPress site.

You should use jQuery instead of $ if you still gets the error do as following.
var j = jQuery.noConflict();
j(document).ready(function(){
j(".showhide").click(function(){
j("nav").slideToggle("slow");
});
});

How jquery $ works without conflict?

In jQuery doc we have such code:
<script src="other_lib.js"></script>
<script src="jquery.js"></script>
<script>
$.noConflict();
jQuery( document ).ready(function( $ ) {
// Code that uses jQuery's $ can follow here.
});
// Code that uses other library's $ can follow here.
</script>
I wonder how this works, Why libs like other_lib.js that uses jQuery's $ works after $.noConflict();. They should not work because global variable $ were removed from global scope.
Thank you.

It is not just that it works after the noConflict call, more importantly if you look at the document ready function it is taking in a variable named $ what jquery is doing when it calls this function is passing in the named jQuery object, which becomes $ in that function's local scope.
Outside of that function calls to $ will not work.
I have done this manually with some self executing javascript in the past and it follows the same pattern:
(function($){
...some page startup code here...
})(jQuery)

Editing a jQuery plugin for matching different jQuery version

I have assigned jQuery.noConflict() to $jq:
var $jq = jQuery.noConflict();
Now I want to edit a jquery plugin to use $jq. There are a lot of codes in the following style:
(function($) { /* some code that uses $ */ })(jQuery)
Changing $ to $jq doesn't solve the problem. What should I do?

You don't need to do anything. The $ is a variable local to the function that wraps the plugin; it's immediately assigned to jQuery, as you can see after the function literal:
})(jQuery) // Immediately calls the wrapper function with jQuery being passed
// as the $ argument.

jquery element not defined, but it used to skip it

I recently transferred a site to a new host. Reloaded everything, and the javascript that worked fine before is breaking at an element it can't find. $('#emailForm') is not defined.
Now, the #emailform isn't on the page, but it wasn't before either, and JS used to skip this and it would just work. Not sure why this is happening. Any clues
Here is the site I am having the prblem:
http://rosecomm.com/26/gearwrench/

jQuery will return an empty jQuery object from $('#emailForm') if there isn't an element with the id='emailForm'.
One of the following is likely true:
You forgot to include jQuery - therefore $ is undefined.
There is another library included that uses $ - in which case you can wrap your code in a quick closure to rename jQuery to $
The Closure:
(function($){
// $ is jQuery
$('#emailForm').whatever();
})(jQuery);
You could console.log(window.$,window.jQuery); in firebug to check for both of these problems.

You have mootools-1.2.2-core-yc.js installed as well, and it is conflicting with jQuery.
http://docs.jquery.com/Using_jQuery_with_Other_Libraries
$(document).ready(function() {
(function($){
// bind 'myForm' and provide a simple callback function
$('#emailForm').ajaxForm(function() {
var txt=document.getElementById("formReturn")
txt.innerHTML="<p>Thank You</p>";
});
...
$(document).ready is being called against the moo tools library instead of jQuery.

I'm not sure why it would be skipped before, but to avoid the error, wrap the statement(s) that reference $('#emailForm') in an if statement that checks to see if it is present:
if ( $('#emailForm').length ) {
// code to handle $('#emailForm') goes here...
}