Eli5 How did classical music composers memorize their songs back then after creating them?

Question

Let’s take for example the nocturnes of Chopin.

My preferred one is nocturne n. 20

He certainly didn’t have studio machine to record their sound AFAIK

How then did he memorize and write down everything to remember later?

Did he start playing the piano, write down the notes, continue playing or did he memorize the whole song by heart without any writing process?

Sorry 4 my bad English btw. Not a English native speaker.

EDIT : thanks everyone for the explanation.

In: 157

Answer 1

They wrote the music down as they came up with it. Composers were all different, but many wrote down themes or melodies they wanted to expand on. Then there are certain ways you can transform themes and move them around and “develop” them as it’s known. Then you might come in after the melody is written and decide how you’d like to harmonize it.