To load default jquery core file from CDN to WordPress, you need to simply copy and paste the following code in your theme’s functions.php file.

function replace_jquery() {
	if (!is_admin()) {
		wp_deregister_script('jquery');
		wp_register_script('jquery', 'https://code.jquery.com/jquery-1.12.4.min.js', false, '1.12.4');
		wp_enqueue_script('jquery');
	}
}
add_action('init', 'replace_jquery');

Have any doubt, then comment here!

To add a new menu/tab to the WordPress toolbar, you need to simply copy and paste the following code in your theme’s functions.php file.

add_action( 'admin_bar_menu', 'add_toolbar_link_top', 999 );
function add_toolbar_link_top( $wp_admin_bar ) 
{	
	$args = array(
		'id'    => 'your-id',
		'title' => 'Your Title',
		'href'  => site_url(),
		'meta'  => array( 'class' => 'your-class-name' )
	);
	$wp_admin_bar->add_node( $args );
}

This code will add new menu in WordPress toolbar.

Have any doubt, then comment here!

WordPress doesn’t have an default option to save modified date. So we have save modified date when user updating their profile.
You can save the modified date by adding the following code in your theme’s functions.php file.

/*Save profile modified date*/
function update_profile_modified_date( $user_id ) {
  update_user_meta( $user_id, 'modified_date', date("Y-m-d") );
}
add_action( 'profile_update', 'update_profile_modified_date' );

You can get this date by using get_user_meta() function. for example see below code.

$user_id=25; // replace your user id here
$modified_date = get_user_meta( $user_id, 'modified_date', true ); 

Have any doubt, then comment here!

We have a filter in WordPress for set url to redirect after logout. You can use this filter to redirect back to current page after logout. Add the following code in your theme’s functions.php file..

/* Logout and return to the page they were on*/
function admin_logout_redirect($logouturl, $redir)
    {
        return $logouturl . '&redirect_to=http://'.$_SERVER['HTTP_HOST'].$_SERVER['REQUEST_URI'];
    }
add_filter('logout_url', 'admin_logout_redirect', 10, 2);

Have any doubt, then comment here!

WordPress added the following code in your header for support emoji.

window._wpemojiSettings = {"baseUrl":"http:\/\/s.w.org\/images\/core\/emoji\/72x72\/","ext":".png","source":{"concatemoji":"http:\/\/your-url\/wp-includes\/js\/wp-emoji-release.min.js?ver=4.2.1"}};
    !function(a,b,c){function d(a){var c=b.createElement("canvas"),d=c.getContext&&c.getContext("2d");return d&&d.fillText?(d.textBaseline="top",d.font="600 32px Arial","flag"===a?(d.fillText(String.fromCharCode(55356,56812,55356,56807),0,0),c.toDataURL().length>3e3):(d.fillText(String.fromCharCode(55357,56835),0,0),0!==d.getImageData(16,16,1,1).data[0])):!1}function e(a){var c=b.createElement("script");c.src=a,c.type="text/javascript",b.getElementsByTagName("head")[0].appendChild(c)}var f;c.supports={simple:d("simple"),flag:d("flag")},c.supports.simple&&c.supports.flag||(f=c.source||{},f.concatemoji?e(f.concatemoji):f.wpemoji&&f.twemoji&&(e(f.twemoji),e(f.wpemoji)))}(window,document,window._wpemojiSettings);

img.wp-smiley,
img.emoji {
    display: inline !important;
    border: none !important;
    box-shadow: none !important;
    height: 1em !important;
    width: 1em !important;
    margin: 0 .07em !important;
    vertical-align: -0.1em !important;
    background: none !important;
    padding: 0 !important;
}

you can remove this WordPress emoji code by WordPress actions. Add the following codes in your functions.php file located in your theme folder.

/*Remove WordPress emoji code programmatically without plugin*/
remove_action('wp_head', 'print_emoji_detection_script', 7);
remove_action('wp_print_styles', 'print_emoji_styles');

remove_action( 'admin_print_scripts', 'print_emoji_detection_script' );
remove_action( 'admin_print_styles', 'print_emoji_styles' );

Have any doubt, then comment here!