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The browser reached code that uses $ before a usable jQuery reference was available. Check that jQuery loaded, then make sure it runs before any plugin or application code that depends on it. If another library uses $, switch to jQuery or a separate alias. A DOM-ready handler cannot fix a missing library or incorrect script order.
What “$ is not defined” means
In jQuery, $ is a shorthand alias for the jQuery function. But JavaScript does not reserve $ for jQuery: another library, a local scope, or a page configuration can leave it unavailable as a jQuery reference. The error text alone does not reveal which cause applies, so start with the failing line and whether the jQuery file actually loaded.
jQuery’s noConflict() API documents that another library may use $ and explains how to relinquish jQuery’s control of that name.
Diagnose the cause before changing code
- Find the first relevant console error. Open your browser’s developer tools and identify the exact line that first fails. Later errors may be consequences of that first failure.
- Check the jQuery request in Network. Look for the script request and confirm its URL is correct and that it completed successfully rather than failing or being blocked. A blocked script fires an error event, as described in MDN’s
<script>reference. - Inspect the rendered script tags. Confirm that jQuery appears before every plugin or application script that calls
$while it is being evaluated. Check the rendered page, not just a template or source file that may differ from what the browser receives. - Check script attributes and execution context. Related scripts marked
asynccan execute as soon as each file is available, with no guaranteed order. If the error occurs only in one bundle, callback, or interaction, inspect that exact line and context: the identifier may not be available in that scope or at that time.
Fix the loading or order problem
If the jQuery request is missing or fails
Correct the script URL or the way the file is delivered, then reload and verify the request succeeds. A dependent script cannot call jQuery if the browser never received and executed the intended jQuery file. Avoid adding a second copy as a guess: jQuery advises against loading two versions, and a duplicate can introduce its own conflicts.
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If dependent code runs before jQuery
Put jQuery before its plugins and application code. For classic external scripts, defer lets the browser parse the document before executing the scripts, while preserving the order of the script elements. Keep all dependent classic scripts deferred and list them in dependency order:
<script defer src="/js/jquery.min.js"></script>
<script defer src="/js/plugin-that-needs-jquery.js"></script>
<script defer src="/js/app.js"></script>This assumes each URL returns the intended file and the plugin and application are compatible with the jQuery version in use. MDN states that deferred scripts execute in document order. Do not rely on that rule for async scripts; remove async from scripts with dependencies or use an explicit dependency-management approach instead.
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This guidance concerns classic scripts. Module scripts defer by default, and the defer attribute has no effect on them. If the page uses modules, verify its module imports and execution context rather than applying classic-script ordering advice blindly.
Resolve a conflict over the $ name
If jQuery is available but $ belongs to another library—or is not available where your code runs—use the full jQuery name. Alternatively, after jQuery loads, call jQuery.noConflict() and use the returned jQuery object under a distinct alias:
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<script src="/js/jquery.min.js"></script>
<script>
var $j = jQuery.noConflict();
$j(function () {
$j(".notice").addClass("ready");
});
</script>Call noConflict() after jQuery has loaded and before using the alias. Then use that alias consistently in the code that needs jQuery. See the jQuery Learning Center’s guide to avoiding conflicts with other libraries.
Choose the fix that matches the evidence
| What you find | Likely cause | What to do |
|---|---|---|
| The jQuery request is missing, failed, blocked, or points to the wrong file | jQuery did not become available | Correct the URL or delivery and verify the request succeeds. MDN |
| jQuery appears after a plugin or application script | Dependency order is reversed | Load jQuery first; preserve that order if using deferred classic scripts. MDN |
Related scripts use async |
They may execute in an unexpected order | Remove async from dependency-bound scripts or use ordered defer or explicit dependency management. MDN |
jQuery exists, but $ resolves to another library or is unavailable in the failing scope |
A name conflict or scoped alias | Use jQuery or set up a noConflict() alias after jQuery loads. jQuery API; jQuery Learning Center |
| The error appears only in one bundle, callback, or interaction | The identifier’s scope or execution timing differs there | Inspect the failing line and execution context; confirm which identifier is in scope. The specific cause depends on the application. |
Retest the behavior that failed
Reload the page after making the change, check the console and Network panel again, and repeat the specific interaction that originally triggered the error. A disappearing console message is not enough: confirm that the dependent plugin or application behavior now works.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why a ready handler is not the fix
A jQuery ready handler waits for the document to be ready; it does not download a missing library, repair a failed request, or make unordered scripts execute in dependency order. First make jQuery available to the failing code, then use a ready handler if the code also needs the DOM to be ready.
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