@tiendungdev “Buying” source code isn’t going to give you the most vital ingredient when it comes to writing code: the why and the how. All you’re seeing is the end result. You‘re not seeing the decisions that went in to arriving at that solutions, the alternatives considered and disregarded, and the pros and cons that were considered between all possible options.
If you want to get better at coding, write more code. Coding is a skill, and like any other skill you get better at it by practicing. You can’t “buy” your way to knowledge.