What is the method to pass a variable from PHP back to JavaScript?

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The method to pass a variable from PHP back to JavaScript is through AJAX (Asynchronous JavaScript and XML) requests. The PHP script can output the variable value as a JSON object or XML data, which can then be processed by JavaScript. The JavaScript code can make an AJAX call to the PHP script, which will return the variable value. The returned value can then be accessed and manipulated by the JavaScript code.