If you are a web developer, you might have encountered the ReferenceError: jQuery is not defined error at some point. This error means that your code is trying to use jQuery, but jQuery has not been loaded yet. There are several possible reasons why this error occurs and how to fix it.
One common reason is that you have placed your jQuery code before the jQuery script tag in your HTML file. For example, you might have something like this:
<script>
$(document).ready(function() {
// some jQuery code
});
</script>
<script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
In this case, your code is trying to use the $ function, which is a shorthand for jQuery, before the jQuery library has been loaded. To fix this, you need to move your jQuery code after the jQuery script tag, or place both of them at the end of your HTML file, before the closing </body> tag.
Another common reason is that you have a typo or a wrong URL in your jQuery script tag. For example, you might have something like this:
<script src="https://code.jquery.com/jqurey-3.6.0.min.js"></script>
In this case, your code is trying to load a non-existent file, which will result in a 404 error and prevent jQuery from being loaded. To fix this, you need to check your spelling and make sure you have the correct URL for the jQuery library.
A third possible reason is that you have a conflict with another library that uses the $ symbol as well. For example, you might have something like this:
<script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/prototype/1.7.3/prototype.min.js"></script>
<script>
$(document).ready(function() {
// some jQuery code
});
</script>
In this case, your code is trying to use the $ function from jQuery, but it has been overwritten by the $ function from Prototype, which is another JavaScript library. To fix this, you need to use jQuery.noConflict() to avoid the conflict and use a different alias for jQuery. For example:
<script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/prototype/1.7.3/prototype.min.js"></script>
<script>
var jq = jQuery.noConflict();
jq(document).ready(function() {
// some jQuery code using jq instead of $
});
</script>
These are some of the most common causes and solutions for the ReferenceError: jQuery is not defined error. I hope this blog post has helped you understand and resolve this error in your web development projects.