If you write a title, then move away from (blur) that input field, WordPress will auto-save a draft for you, likely in order to create a post slug placeholder for you.
I’m looking to possibly extend this functionality to also save on blurring of the content body TinyMCE pane. The logic is not entirely straightforward — for example, it appears to saves a draft only when the post is yet unpublished — so I need to look further into the logic.
In order to scope this change, I need to find where in the JavaScript (?) codebase WordPress does this auto-saving. Having trouble so far. Does anyone know?
I believe the file responsible is
wp-includes/js/autosave.js. There is a dev version for easy reading.