PHP variable inside a javascript "text change onclick" : Hi I have this javascript code inside a PHP echo

            function change_text()
                {
                    if(document.getElementById(\"toggle_button\").innerHTML==\"Ver respuesta\")
                    {
                        document.getElementById(\"toggle_button\").innerHTML=\"$PHP_VARIABLE\";
                    }
                    else
                    {
                        document.getElementById(\"toggle_button\").innerHTML=\"Ver respuesta\";
                    }
                }

I need to insert the text of $PHP_VARIABLE at $PHP_VARIABLE, but it is not working...
I think this will work with this javascript code who obtain the variable, but I don't know how to insert this in the code.

    var php_var = "<?php echo $php_var; ?>";