か～ないかのうちに

The grammar structure か～ないかのうちに expresses that something happens immediately after – or practically at the same time as – a preceding action. It emphasizes that the second event occurs so quickly that the first action has barely been completed (or may not even be fully completed yet). It often translates to "just as," "barely had … when," or "no sooner had … than."

The structure repeats the same verb in both its dictionary form and its ない-form, creating a sense of "whether (the action happened) or not":

This pattern highlights the speed and immediacy of the second event. The speaker is often surprised or impressed by how quickly things happened.

Usage notes

• The verb used before か and before ないか is the same verb. The dictionary form comes first, then the ない-form follows.
• The clause after のうちに describes something that happened unexpectedly quickly or almost simultaneously.
• This pattern is mainly used to describe past events and is common in written or narrative Japanese. It carries a somewhat literary or dramatic tone.
• A similar grammar point is 〜～たとたん, which also means "the moment …" but does not carry the same nuance of "barely even finishing" the first action. か～ないかのうちに places stronger emphasis on the incompleteness of the first action when the second event occurs.

Shortened form

In practice, the ないか portion is sometimes omitted, leaving just Verb + かのうちに, though the full form is more standard.