I promise you.. (something you will do for him/her) Example: I promise you will have an Ipad next month. I promise to you.. (giving him assurance about something) Example: I promise to you that I will be your friend forever.

I promise you is correct 🙂

The other answers are correct, but you can also say "I will make a promise to you..." So you might hear that sometimes.

Context is needed. I promise you, you can learn this if you practice. I promise to you, i will be there for you.

I promise you