Uncaught ReferenceError: $ is not defined
jQuery is a JavaScript library and the purpose of jQuery is to make code much easier to use JavaScript. When you are working with the jQuery library , then there is a pretty good chance that you will encounter the following jQuery/JavaScript error at some point in time:
Basically $ is an alias of jQuery() so when you try to call/access it before declaring the function, it will endup throwing this $ is not defined error . This usually indicates that jQuery is not loaded and JavaScript does not recognize the $. Even with $(document).ready , $ is still going to be undefined because jquery hasn't loaded yet.
To solve this error:
Load the jQuery library at the beginning of all your javascript files/scripts which uses $ or jQuery, so that $ can be identified in scripts . example In the following code, you can see that the jQuery library is loaded after the script. So, you will get "$ is not defined" error.
<!DOCTYPE html>
<html>
<head>
<script>
$(document).ready(function(){
$("p").click(function(){
alert("You Clicked....");
});
});
</script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
</head>
<body>
<p>Click Here...</p>
</body>
</html>
In order to fix this error, include the jQuery library file before the JavaScript code.
<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script>
$(document).ready(function(){
$("p").click(function(){
alert("You Clicked....");
});
});
</script>
</head>
<body>
<p>Click Here...</p>
</body>
</html>
Browser ViewClick Here...
Working offline
There may be a chance where you are working offline but trying to loading or referring the jQuery code from internet . In this case, there is a problem with the internet connection and jQuery will not load from the CDN . In this case, you can simply download the jQuery.js and use it locally rather then downloading from internet and use the code below to load jQuery locally :
<script src="/js/jquery.min.js"></script>
Conflict with Other Libraries
As you already know jQuery uses the $ sign as a shortcut for jQuery. There are many other popular JavaScript frameworks like: Angular , Backbone, prototype.js, MooTools, and more. Thus, if you are using another JavaScript library that uses the $ variable, you can run into conflicts with jQuery. By using noConflict() you can of course still use jQuery, simply by writing the full name (jQuery) instead of the shortcut:
<script>
$.noConflict();
jQuery(document).ready(function(){
jQuery("button").click(function(){
jQuery("p").text("jQuery is still working!");
});
});
</script>
Path to jQuery library you included is not correct
You might have put an incorrect path to jQuery library , or there may be typo in your file.
<script src="ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
The above code does not include the HTTP: or HTTPS: in the src attribute but the browser, FireFox, needed it so you should changed it to:
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
The jQuery library file is corrupted
If the jQuery library file has been downloaded from an untrustworthy sites and the file is corrupted, this error may happen.
Google CDN:
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
Microsoft CDN
<script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.3.1.min.js"></script>
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