politeとassertive：緊急度を選ぶ

A live region is an element a screen reader watches, so it speaks any text that changes inside it without the user moving focus there.

The aria-live attribute has two useful values you will reach for constantly: polite and assertive. They decide how an update is delivered. 🔊

With polite, the screen reader finishes whatever it is saying, then reads your update. It never cuts the user off mid-sentence.

With assertive, the screen reader stops what it is reading and announces your update right away. Use it only when waiting would cost the user.

Reach for polite almost every time. Save, sort, filter, and progress updates can all wait a beat without confusing anyone.

Use assertive only for things the user must hear immediately, like a failed payment or a session about to expire.

The value off tells the screen reader to ignore changes in that element. It is the implicit default for elements you have not marked as live.

The live element should be in the DOM before the text changes. Screen readers watch existing regions, so add it empty and fill it later.

Announce by updating the text content inside the existing region. Swapping the whole region out can make the announcement silently fail.

Fire several assertive updates fast and they fight each other, interrupting and talking over the last one. Polite queues them in order instead.

Pick the level by asking how much an interruption helps. Most updates: polite. Errors and warnings the user must act on: assertive.

You add a small confirmation that a list was sorted. Which politeness level fits best?

You learned that polite waits and assertive interrupts. Default to polite, reserve assertive for true urgency, and keep the region in the DOM. ✅