Why is my jQuery code throwing a ''$' is not defined' error?

JQuery: Handling the "'$' is not defined" Error

Problem Statement

A simple JQuery click event fails to execute, throwing a "$ is not defined" error. Despite referencing the JQuery script in the site.master, the error persists.

Possible Causes and Solutions

This error can stem from three primary sources:

1. Improper JavaScript Loading:

   • Ensure the JavaScript file is referenced correctly with its full path, including the ".js" extension.
   • Verify that the script is not loading asynchronously or deferred, as JQuery requires a synchronous load.

2. Corrupted JQuery Version:

   • Check that the JQuery version is intact and not modified or overwritten by plugins.
   • Reference the JQuery library directly from a CDN to rule out local file issues.

3. Premature JavaScript Execution:

   • Use the $(document).ready() or jQuery(function() {...}) syntax to encapsulate JQuery code.
   • Ensure that the JQuery initialization occurs after the document has fully loaded.

Troubleshooting Steps

• Inspect the site.master to confirm the正確filepath of the JQuery script.
• Use Firebug's "net" panel to check if the script is loading successfully.
• Move JQuery-dependent code within a $(document).ready() block.
• Avoid loading plugins before the JQuery core.

Additional Considerations

Code that does not rely on JQuery can be separated using document.readyState to enhance performance. By following these steps, you can resolve the "$ is not defined" error and ensure the proper functioning of JQuery in your application.

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