I am trying to allow a plugin to modify the rendered content of posts prior to it being rendered for the WP API, or at least save it as a separate property on that JSON response.

For instance, imagine a plugin that changes the content of a post from

Here is some content : foo


Here is some content : bar

It's setup to use the the_post filter to make its modifications for the frontend. But the REST api is unaffected. I have tried using the rest_prepare_post filter but it's (a) apparently a bad practice to modify the rendered content directly, so I'd put it as an additional property? and (b) difficult to work with -- if I so much as try to assign $data->$data['content']['rendered'] to a variable I get the message that I am trying to convert a WP Rest response object to a string. Yet if I output that same variable to my error log, it works fine.

add_filter( 'rest_prepare_post', array( __CLASS__, 'beforeFilterRest' ), 0, 2 );

public static function beforeFilterRest( $data, $post ){

            $old_rendered_content = $data->$data['content']['rendered'];
            $data->$data['content']['rendered'] = preg_replace_callback(
                array( __CLASS__, 'substituteToken' ),
            return $data;

I get an error right at the first line of that function. What am I missing?

1 Answer 1


It looks to me like you've written $data->$data[...] where you mean to have $data->data[...]. The "object to string" conversion error is probably due to the second $data, where PHP expects an object's property name but is getting another reference to the $data object.

  • 3
    Let's never speak of this again..
    – tmdesigned
    Sep 16, 2018 at 8:48
  • 1
    I once wrote a the_content filter that blanked every page but the one I was trying to filter. In the end I discovered that my return $content; line was only happening where my condition matched (ie, it was inside the if() statement). An easy fix, but I spent five solid hours barking up all the wrong trees before I noticed my mistake.
    – Pat J
    Sep 16, 2018 at 16:56

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