How accomplish modification the_content if home/start page?

Question

How can I modify the_content if the page is the home/start page?

I thought this could be done through a function in functions.php, but soon realized after some googling that the functions.php -file runs before parse query, so WP doesn't now if it is the home/start page or not.

What I want to do: If the post have one or multiple images in it, grab the first image and display it in the loop before the content of the post on the home/start page. I don't want to go with "Featured image".

How do I accomplish this?

Answer 1

You can check for is_home() and is_front_page() inside of your filter:

add_filter( 'the_content', function( $content ) 
{
    if ( ! is_home() and ! is_front_page() )
        return $content;

    return 'Home, sweet home!<br>' . $content;
});