Get first category name or id from wordpress post

get-first-category.php

<?php
	// in the loop
	$category = get_the_category();
	$currentcat = $category[0]->cat_ID;
	$currentcatname = $category[0]->cat_name;
	$currentcatslug = $category[0]->slug;

	// outside the loop
	global $post;
	$categories = get_the_category($post->ID);
	$currentcat = $category[0]->cat_ID;
	$currentcatname = $category[0]->cat_name;
	$currentcatslug = $category[0]->slug;
?>