How to set up a post word limit for a custom post type

Question

I'm not trying to set the exerpt for a custom post type, but a word limit in the admin of my custom post type.

I have just set up a custom post type:

add_action( 'init', 'test_post_type' ); 
function create_post_type() 
    register_post_type( 
       'test_post_type',
        array(
            'labels' => array(
                'name' => __( 'test' ),
                'singular_name' => __( 'test' )
            ),
            'public' => true,
            'has_archive' => true,
        )
    );
}

I would like to find out how to set a word limit for this custom post type, so when the publish button is clicked, it will display an error due to the amount of words going over the word limit.

I only know how to set up a word limit for the title on all posts:

function maxWord($title){
global $post;
$title = $post->post_title;
if (str_word_count($title) >= 15 ) // maximum of 15 words
    wp_die( __('Your post title is over the maximum word count.') );
} 
add_action('publish_post', 'maxWord');

I would like it the same as above, but a word limit on the tinymce post in my custom post type only.

Any help much appreciated.

Answer 1

Filters and Actions

The hooks you can chose to run whatever limits the post content length from, is either save_post, save_post_{post_type} or edit_post (or both) (the following actions are executed inside wp_publish_post()

/** This action is documented in wp-includes/post.php */
do_action( 'edit_post', $post->ID, $post );
do_action( "save_post_{$post->post_type}", $post->ID, $post, true );
do_action( 'save_post', $post->ID, $post, true );
do_action( 'wp_insert_post', $post->ID, $post, true );

or one of the post transition hooks executing inside wp_transition_post_status(). Namely those are:

do_action( 'transition_post_status', $new_status, $old_status, $post );
do_action( "{$old_status}_to_{$new_status}", $post );
do_action( "{$new_status}_{$post->post_type}", $post_id, $post );

To check inside a callback on an filter or action if you are on the correct filter, you can use current_filter() or current_action() (where later is just a wrapper for current_filter()), which returns a string with the name of the filter or action currently running.

Limits

To limit the amount of words, you may want to use

wp_trim_words( $content, 300 );

to limit the content to for e.g. 300 words.

There is more to it when there is already content present. To get around this, you can leverage the plugins in this answer I wrote to limit excerpt length. Just alter it if you want to run it on the content only.

The general idea (in pseudo code) always is:

Explode the string of words in an array on empty space
Count the number of array items
If they exceed $limit, loop through them or slice the array
Return everything below and equal to the threshold

Core API

The reason why you may want to use wp_trim_words() instead of a simple loop is, that it strips all HTML tags from a string (so they don't add to the count) and that there is a filter running callbacks before the result is returned, allowing for a very fine grained and targetted approach

apply_filters( 'wp_trim_words', $text, $num_words, $more, $original_text );

Putting a plugin together

Just fill in whatever you may want to do. Make sure that you inform the user properly by using something like post_updated_messages to tell the user why you stripped off words, refused to save the content or whatever UX you want deliver

<?php 
/** Plugin Name: WPSE (#172544) Limit Content by Word Count */

add_action( 'save_post_test_post_type', function( $id, \WP_Post $post, $updated ) 
{
    # debug:
    # var_dump( $post, $_POST );
    // Here you can do whatever you want to do to limit the 
}, 10, 3 );

Answer 2

Personally I would not recommend making any such changes to the default way the Wordpress editor works as it could pose issues in the future.

However, I think you may be able to accomplish this with some Javascript/jQuery.

Take a look at this example. Make sure to test suggested implementation thoroughly, I have not tested it.