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How to Ensure that jQuery is only loaded once

26. July 2016 13:50 by admin in ASP.NET, C#, Jquery

Often we have pages and master pages and "bundles" that load scripts like jQuery and we can't always be sure that a particular page already has it loaded. Here is a script that will only inject jQuery into a page if it has not already been loaded:

<HTML>
<HEAD>

<!-- comment or uncomment next line to test it out --->
<script src='https://code.jquery.com/jquery-3.1.0.min.js'></script>

<script>

// Only do anything if jQuery isn't defined

if (typeof jQuery == 'undefined') {

function getScript(url, success) {

var script = document.createElement('script');

    script.src = url;

var head = document.getElementsByTagName('head')[0],done = false;

// Attach handlers for all browsers

script.onload = script.onreadystatechange = function() {

if (!done && (!this.readyState || this.readyState == 'loaded' || this.readyState == 'complete')) {

done = true;

// callback function provided as param

success();

script.onload = script.onreadystatechange = null;

head.removeChild(script);

};

};

head.appendChild(script);

};

 

getScript('https://code.jquery.com/jquery-3.1.0.min.js', function() {

if (typeof jQuery=='undefined') {

// Super failsafe

} else {

alert("We Loaded it!");

// jQuery loaded 

}

});

 

} else { 

// jQuery was already loaded

alert("jQuery is Already Loaded!");

// Run your jQuery Code

};

</script>

</HEAD>

<BODY>

</BODY>

 

</HTML>

 

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