If you want to remove woocommerce related products programmatically in WordPress then add that following code in your functions.php file.
Clear the query arguments for related products so none show.

function woocommerce_remove_related_products( $args ) {
	return array();
}
add_filter('woocommerce_related_products_args','woocommerce_remove_related_products', 10); 

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If you want to hide sale flash content in woocommerce then add that following code in your functions.php file.

add_filter('woocommerce_sale_flash', 'woocommerce_custom_hide_sales_flash');
function woocommerce_custom_hide_sales_flash()
{
    return false;
}

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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');

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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.

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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 ); 

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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);

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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' );

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If you want to get Product id from order id in Woocommerce then fetch order details.

$order = new WC_Order( $order_id );
$items = $order->get_items();

then if you loop through them, you can get all the relevant data:

foreach ( $items as $item ) {
    $product_name = $item['name'];
    $product_id = $item['product_id'];
    $product_variation_id = $item['variation_id'];
}

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