ないうちに (nai uchi ni): Before an event or change occurs

Before something happens; while it has not yet happened

Negative nai-form verb + うちに, followed by an action done before that event or change occurs.

Do something while a situation still holds, before a change or an often unwanted event occurs. The expression emphasizes using the remaining opportunity, rather than merely ordering two events in time.

雨が降らないうちに、洗濯物を取り込みましょう。

Let us bring in the laundry before it rains.

忘れないうちに、電話番号をメモしました。

I wrote down the phone number before I could forget it.

スープが冷めないうちに、飲んでください。

Please drink the soup before it gets cold.

店が混まないうちに、昼ご飯を食べに行きます。

I will go for lunch before the restaurant gets crowded.

暗くならないうちに、山を下りましょう。

Let us descend the mountain before it gets dark.