Syntax

get_post_type( int|WP_Post|null $post = null )

Usage

It returns a string of the post type of the post ID or the current post, from this value you can check on the post type to decide what you do with it, just like the code.
Add the below code to the wp-includes/post.php

function get_post_type( $post = null ) {
  $post = get_post( $post );
    if ( $post ) {
        return $post->post_type;
  }
    return false;
}