jQuery is not defined, working on local server but not online

Question

here's my problem:

Chrome console:

    Uncaught ReferenceError: jQuery is not defined jquery-ui.min.js:6
    Uncaught ReferenceError: jQuery is not defined slider.js:1
    Uncaught ReferenceError: jQuery is not defined functions.js:1
    Uncaught ReferenceError: jQuery is not defined menu_mobile.js:1
    Uncaught Error: Bootstrap's JavaScript requires jQuery 

I enqueue my scripts before wp_head() in header.php:

<?php
        function frontEnd_scripts() {
            wp_enqueue_script("jquery");
            wp_deregister_script('jquery.mobile');
            wp_register_script('jquery.mobile', ("//ajax.googleapis.com/ajax/libs/jquerymobile/1.4.3/jquery.mobile.min.js"),array('jquery'));
            wp_enqueue_script('jquery.mobile');
            wp_register_style('jqm_css',('//ajax.googleapis.com/ajax/libs/jquerymobile/1.4.3/jquery.mobile.min.css'));
            wp_enqueue_style('jqm_css');

        }
        add_action('wp_enqueue_scripts', 'frontEnd_scripts'); 
    ?>
    <?php wp_head(); ?>
    <!-- My custom scripts here -->

I tried to enqueue my custom scripts with no results.

js files wrapped like this:

jQuery(document).ready(function($j){
    // Do some stuff
});

Everything works fine on a local MAMP server but it does not work on web server and the only way I can make it work is to hardcode the jQuery script tag before the wp-head(). Is it possible that my online version of wordpress don't have jQuery included or removed ?

Thanks !

Answer 1

Add this in functions.php instead of header.php

function frontEnd_scripts() {
    wp_enqueue_script("jquery");
    wp_deregister_script('jquery.mobile');
    wp_register_script('jquery.mobile', ("//ajax.googleapis.com/ajax/libs/jquerymobile/1.4.3/jquery.mobile.min.js"),array('jquery'));
    wp_enqueue_script('jquery.mobile');
    wp_register_style('jqm_css',('//ajax.googleapis.com/ajax/libs/jquerymobile/1.4.3/jquery.mobile.min.css'));
    wp_enqueue_style('jqm_css');
}
add_action('wp_enqueue_scripts', 'frontEnd_scripts');