Can someone explain me this autocomplete code and tell me how to make something like it.

Question

https://code.sololearn.com/WH6KJ2V7E8xX/?ref=app

HERE IS THE CODE WHICH I WANT TO UNDERSTAND

Answer 1

Its working is as follows:
1. When DOM content is loaded, it calls an anonymous function.
2. That functions adds an event listener to text area.
3. This listener responds to input.
4. This listener searches for HTML:5
5. Replaces HTML:5 with predefined code. Found using js method includes.
6. The predefined code is stored in variable HTMLTemplate in base64 format.
7. That code is first decoded and then used to replace HTML:5

Answer 2

Can you give me some example I am not clear 😵😵