GeolocationCoordinates：altitude 屬性
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since 2020年7月.
Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.
GeolocationCoordinates 介面的 altitude 唯讀屬性是一個 double 值，表示位置相對於 WGS84 橢球（定義名義海平面）的高度（以公尺為單位）。如果實作無法提供此數據，則此值為 null。