expression, adverb
no sooner than; as soon as; immediately after
Used after the past tense of a verb to express that one action happens right after another, often with a sense of surprise or immediacy. Common in written or formal Japanese.
彼は家に着いたかとみると、すぐにまた出かけた。
No sooner had he arrived home than he went out again.
雨がやんだかとみると、また降り出した。
The rain had barely stopped when it started again.