Is said whole, with nothing composed onto it and takes no だ／です, so there are no forms to conjugate.

やった！やった

yattaI did it!expression

Example sentences2

第一希望だいいちきぼうの会社かいしゃに受うかった!やった!

daiichikibou no kaisha ni ukatta! yatta!

I got into my first-choice company! I did it! casual

探さがしてた鍵かぎ、見みつかった!やった!

sagashiteta kagi, mitsukatta! yatta!

I found the keys I was looking for! I did it! casual