How to restrict text length of a field while in WordPress editor?

Question

I would like to restrict the fields while creating a new post in WordPress. For the title, it should not exceed 40 characters. For the content, it should not exceed 400 characters. If these maximum values are exceeded, I would like to show an error message and not let the user continue. How do I do that in WordPress?

Answer 1

You should be able to use wordpress filters to modify the code that gets outputted when the editor is called. Essentially you would want to use it to insert some javascript and an extra div tag to display your error, then just read the contents of the "editorcontainer" id and show the error once it reaches a certain character limit.

I don't have the time at the moment to write a case example, but depending on your skill level, the functions you are looking for are:

 apply_filters("the_editor", "customfunction_limitarea");

Where customfunction_limit area is your created function to insert the javascript. You can see how the_editor is currently called and how the default filters are applied in "wp-includes\general-template.php" on line 1822. The default looks like this:

$the_editor = apply_filters('the_editor', "<div id='editorcontainer'><textarea rows='$rows'$class cols='40' name='$id' tabindex='$tab_index' id='$id'>%s</textarea></div>\n");

I would try modifying that statement by placing a new filter in a functions.php file located in your themes directory, that way you don't have to worry about it getting over-written during an update. Otherwise, if you absolutely have to edit the wordpress core (generally a no-no), general_template.php would be the place to do it I think.

Essentially just read up on wordpress filters a little bit (be warned there's not a ton of documentation or examples available for it other than the basic stuff), and that should provide everything you need. The input verification end is easy enough to find scripts, just google jquery post limiting. Something like this might be exactly what your looking for:

http://swiki.fromdev.com/2010/02/jquery-maximum-limit-texttextarea-with.html