Handling Errors

While using the Core APIs, it’s a good idea to check return values. For example, when creating a post, if something goes wrong you should be able to handle that outcome. Not handling errors and failures can lead to unstable code and unpredictable behavior.

Return values

Many functions return error and success values. You should always check these values after making a call. For example get_post_meta returns a custom field value, but if that custom field/post meta does not exist, it returns an error value.

Different APIs return different error values, and can include:

  • null values
  • false
  • WP_Error objects

WordPress API calls at the time of writing do not throw exceptions. However if you hook into actions such as save_post and throw an exception, it may not be caught due to this expectation, so do not throw exceptions unless you’re sure you know what you’re doing.

WP_Error

The WP_Error object is a catch all error message object returned by some APIs. It has internal storage for multiple error messages and error codes.

is_wp_error

This is a helpful method to simplify error checking. It checks if a returned value was a WP_Error object, and also checks for a handful of other error values. It returns a true or false value, allowing checks such as these:

This is a helpful method to simplify error checking. It checks if a returned value was a WP_Error object, but does not check for other error values. It’s shorthand for if ( get_class( $variable ) == 'WP_Error' ). For example:

  1. if ( !is_wp_error( $value ) ) {
  2.     // do things
  3. } else {
  4.     // display a warning to the user and abort
  5. }

While this is a useful function, remember, not every API returns the same error value, and you should check first.