How is the script implemented without pressing a button?

Question

Programming

Hello.
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I often noticed that even before pressing the button, files and records are somehow miraculously saved, even if I reload the page, or say, close it, and then open it again in the same place, my incomplete form will be at that stage of completion , which was, file attachments, text. I found the same thing in the settings in the sites, checked the box, and the function is already connected, removed it - disabled.
I'm especially interested in what kind of product filtering
works on. I have a question about technologies, I want to know exactly what it's done on. We need the opinion of experts, especially those who implement this functionality on Yii2.
I have an assumption that this is node.js, ajax - but I need to know for sure, maybe you have documentation, manual, please share it with me. I have been wanting to learn these technologies for a long time.

Answer 1

This is LocalStorage.