GeolocationCoordinates：speed 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 speed 唯讀屬性是一個 double 值，表示裝置的速度（單位為公尺每秒）。如果無法測量，則此值為 null。