also: よっしゃー
interjection
Colloquial interjection expressing understanding, agreement, or readiness. Often used when one has grasped something or is about to start an action. Similar to よし, but more casual and energetic.
「これ、お願いね。」「よっしゃ、任せて！」
"Can you handle this?" "Gotcha, leave it to me!"
よっしゃ、やるぞ！
Alright, let's do this!
よし is more standard and slightly more formal; よっしゃ is a colloquial, energetic variant often used among friends or in casual situations.
Colloquial variant of よし, with emphatic gemination and sometimes a prolonged final vowel.