the_category_ID() WP 0.71

Deprecated in 0.71. It is no longer supported and can be removed in future releases. Use get_the_category() instead.

Returns or prints a category ID.

No Hooks.

Return

Int. Category ID.

Usage

the_category_ID( $echo );

$echo(true/false)

Whether to echo the output.
Default: true

Code of the category ID: wp-includes/deprecated.php ^{WP 5.2.2}

<?php
function the_category_ID($echo = true) {
	_deprecated_function( __FUNCTION__, '0.71', 'get_the_category()' );

	// Grab the first cat in the list.
	$categories = get_the_category();
	$cat = $categories[0]->term_id;

	if ( $echo )
		echo $cat;

	return $cat;
}