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Avoid requesting the same external script twice

I request an external script by adding this to my HTML file:
<script>
$(document).on("turbolinks:load", function() {
$.getScript("https://example.com/script");
});
</script>
Say the content of the script is as follows:
doSomething = function() {
// ...
};
My website is a Ruby on Rails app with Turbolinks, which caches the content of the requested script between page visits. My script tag does not know about this, so if I revisit the page it will request the script again. How do I avoid this? My current solution is to check if the scripts content is known:
<script>
$(document).on("turbolinks:load", function() {
if (!window.doSomething) {
$.getScript("https://example.com/script");
}
});
</script>
But this depends on the content inside the script staying the same. So I would rather check if a script from the source https://example.com/script already exists? Or maybe some other approach. Any ideas?

Like epascarello commented, $.getScript appends to head so check that it's not in head before getting it.
if (!$('head script[src^="https://example.com/script"]').length){
$.getScript("https://example.com/script");
}
Use the Attribute Starts With Selector because $.getScript appends a timestamp to avoid getting an already cached version, i.e. it requests a new URL each time.
If you're going to use it more than once:
function getScriptOnce(url){
let selector = 'head script[src^="' + url + '"]';
if (!$(selector).length){
$.getScript(url);
}
}
getScriptOnce("https://example.com/script");

WordPress Contact Form 7 Plugin behaves strange when it is part of AJAX-loaded content

I am currently trying to implement the WordPress Contact Form 7 Plugin into a WordPress-site I created. The theme uses jQuery to overwrite the default link behaviour and AJAX to load the requested page without actually reloading the whole page.
The problem is: The contact form works perfectly when the page where it is used on is loaded directly. However, if the page is loaded via AJAX, there are two strange behaviours: The Google reCAPTCHA widget is not showing up and after submit, instead of showing the div with the success-message, I am redirected to the themes "404" page. The mail gets sent successfully though. I use the plugin/contact-form in AJAX mode - so it makes an AJAX call itself to submit the data and handle the response without page refresh.
I am a bit overwhelmed where to start to solve this problem. Just for testing, I tried to hardcode all scripts from the direct pageload to the theme, so that they are also there when the contact-page is loaded via AJAX. Unfortunately, this didn't have any effect at all. I also tried to call the wpcf7InitForm() function of the plugin, as it was suggested in another question here - also with no success.
This is my ajaxload-script:
jQuery(document).ready(function($) {
// Targeting all internal links
$(document).on('click', 'a[href^="http://' + top.location.host.toString() + '"]:not([href*="wp-admin"])', function(event) {
event.preventDefault();
var url = $(this).attr('href');
$.ajax(url, {
beforeSend: function() {
if ($('#ajax-loader').length == 0) { $('body').append('<div id="ajax-loader"></div>'); }
$('#ajax-loader').fadeIn();
// Dimming static elements during loading
$('#mainbar').animate( { opacity: '0.5' } );
},
success: function(data) {
var data = $('<div />').html(data);
window.history.pushState('...', '...', url);
document.title = $(data).find('title').text();
$('#mainbar').html($(data).find('#mainbar > *'));
// Undoing design modifications to static elements
$('#mainbar').animate( { opacity: '1' }, 150 );
$('body').triggerHandler('reflow');
},
});
});
});
Help on this topic would be really appreciated and thanks in advance!

Couple ideas after reading through some stuff:
Might be a bug with the recaptcha - looks like the latest version specifically fixes recaptcha problems (not sure if they are yours though): http://contactform7.com/2015/11/23/contact-form-7-431/#more-16357
The div not showing up should be easy to debug by using absolute paths. In Wordpress, I usually use the bloginfo(); function. Try putting something like this in your form submit success callback to test path visibility between the AJAX and non-AJAX pages:
<?php
$pathCheck = bloginfo('template_directory');
echo $pathCheck;
?>
The problem with the div not showing up could also be how you are structuring the callback. From this question, it appears that the plugin has specific callback hooks you have to use that aren't in the documentation:
$(".your-form-class").on('wpcf7:mailsent', function(event){
// Show success div code would go in here
});
Great question btw. You used proper english and clearly explained your problem, pretty rare on S.O. Hope some of this gets you going.

remove script tag from ajax response data

i am working on a single page application using jQuery. whole html pages are sent as response to browser as ajax response.
$.post(url, function (data) {
$("#resp").html(data);
$("#resp").find("script").each(function (i) {
//alert($(this).text());
eval($(this).text());
});
});
how to remove script tags from data and than assign html to the div ?
the issue i am facing is the scripts that are written in the response page. they were not getting added to the DOM at first, so i used eval(), now the scripts are getting added twice in some situations.

The easiest way would be to use the .load() function with a fragment selector, since that will strip out <script> tags prior to updating content and result in them not being executed. If you're working with entire HTML pages though there may not be a suitable selector for you to use. However, I'd suggest trying this first:
$('#resp').load(url + ' body');
That would give you just the content between the <body> and </body> tags in the HTML page requested via AJAX.
If that doesn't work, I guess you could try manually stripping out <script> tags from the response prior to adding to the DOM:
$.post(url, function(data) {
var tempDiv = $('<div>').html(data).find('script').remove();
$('#resp').html(tempDiv.html());
});
That creates a new <div> element that isn't part of the document, sets its HTML to the returned HTML from the AJAX request, searches for <script> elements inside that, and then removes them. However, even though the element isn't part of the current document yet, the scripts may still end up being executed (I've never had a reason to do this so I haven't tested it).

with the help of Anthony's answer this is what i did to get it working :
$.post(url, function (data) {
var tempDiv = $('<div>').html(data);
var raw = $('<div>').html(data);
$(tempDiv).find("script").remove();
$("#resp").html(tempDiv.html());
$(scripts).find("script").each(function (i) {
//alert($(this).text());
eval($(this).text());
});
});
i could not understand why
var tempDiv = $('<div>').html(data).find('script').remove();
did'nt work though.

jQuery load with variable instead of element id

i've got a slight jQuery problem.
What i want is to load a particular area of an external html doc into a div,
instead it loads the whole document, not the specified area.
This is the trigger:
$('a').click(function(){ // my link to trigger the load
var pid = $(this).attr('href'); //the pid is the links href
getproject(pid); //trigger the load function, pass variable
});
This is the triggered function:
function getproject(pid) {
$('#container').load('data.html', pid);
}
So when i click my link, it should load the element with the id (#) specified by the link into my container, but it loads the whole data... i cant seem to find a solution to this.
The Link looks like this (cant use exact markup here):
a href="#elementtoload"
The data document looks like this:
div id="elementtoload"
div id="..."
and loads of more elements with content, which should be loaded by id from the links href.

Looking at the documentation for $ load, you should be able to do this:
function getproject(pid) {
$('#container').load('data.html #' + pid);
}

http://api.jquery.com/load/
Second section, Loading Page Fragments. For us to say exactly how this is relevant, you'd need to provide an example of the triggering link, and ideally the document you're loading.

Not sure what your actual intent is but it seems to me that you are going to alot of trouble to get the pid but then not using it in your load routine. I'm guessing the code should look more like this:
function getproject(pid) {
$(pid).hide().load('data.html');
}

String concatenation:
.load('data.html ' + pid);
Regarding your update:
<div id="#elementtoload"> should be <div id="elementtoload">

I was trying something similar and after some hours (...) michael came finally with something that works :) this did the trick for me, the # should be in the url string, like this:
$('#div1').load('data.html #' + x);

JQuery load() will break facebook like button/comment box. How to workaround?

I am coding a big website but I have cut down my problem into the following tiny html file:
http://dl.dropbox.com/u/3224566/test.html
The problem is that if I (re)load with JQuery a content that features a facebook code, the latter won't appear, even if I reload the script (leading to a duplication of that all.js script, which is another issue).
How can I fix this?
Regards,
Quentin

Use the FB.XFBML.parse() docs after you load the new content
function loadPage() {
$('#test').load('test.html #test', function() {
FB.XFBML.parse( );
}).fadeOut('slow').fadeIn('slow');
}
Note, that loading a fragment with id test in a div with id test will create multiple (two) elements with the same id (nested in each other) in the page, which should never happen as it is invalid.
To avoid this use the more verbose $.get method
$.get('test.html',
function(data) {
var temp = $('<div>').html(data).find('#test');
$('#test').html(temp.html());
}
);