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Pre-populating the form field with Wordpress post title
Is that all of your code? If so, "post_title" is not defined anywhere. Also, if you put the title of the page/post into your "message" that an end-user can edit and remove, what is the point? If you are trying to grab a value from the page I would recommend storing it as a hidden value on the form so that it cannot be overwritten by the user. If you just want the basic title from the HTML you could reference the "document.title" from the DOM and eliminate defining your "post_title" field altogether, but it depends on your application or if there's anything else you are trying to do with your setup.