interjection
Casual, energetic affirmative response to a request or suggestion, often used by men. Implies readiness and willingness.
「手伝ってくれる？」「よしきた！」
"Can you help me?" "You got it!"
「もう一杯どう？」「よしきた、もらおう。」
"How about another drink?" "All right, I'll take one."